Method and apparatus for force redistribution in articular joints

ABSTRACT

Pathologies of joints arising from improper force distributions are addressed by displacement of targeted connective and muscle tissues surrounding the joint in order to realign force vectors and alter moment arms loading the joint.

RELATED APPLICATIONS

The present application claims the benefit of priority of U.S.provisional application No. 61/237,518, filed Aug. 27, 2009, and of U.S.provisional application No. 61/288,692, filed Dec. 21, 2009; both ofwhich applications are incorporated by reference herein.

FIELD OF THE INVENTION

The present invention generally relates to the field of orthopedics. Inparticular, the present invention is directed to an interventionaltechnique and an implant for redistributing forces within articularjoints to provide a therapeutic effect.

BACKGROUND

The human body contains many joints that permit articulation of varyingdegrees between bones. Those that permit free articulation are referredto as diathroses. Examples include the hip, knee, elbow and shoulder. Avariety of connective tissues are associated with the diathroses joints,including intra-articular cartilages that provide cushioning and smoothsliding surfaces, ligaments that provide flexible connections betweenbones and tendons that slide over joints and connect the muscles toprovide motion. When connective tissues are compromised, joint pain andloss of function can result.

One example of compromised connective tissue is osteoarthritis of theknee or knee OA. Knee OA is one of the most common causes of disabilityin the United States. OA is sometimes referred to as degenerative, orwear and tear, arthritis. The knee joint is formed by the articulationof the femur, patella, and tibia (see FIG. 3). Like other freelyarticulating joints, the knee joint is enclosed by a fibrous jointcapsule, lined by a synovial membrane. The inferior surface of thepatella articulates with the femoral surface forming the patellofemoraljoint. The distal end of the femur has two curved articular surfacescalled the medial and lateral condyles. These surfaces articulate withthe medial and lateral tibial condyles, forming the tibiofemoral joint,which flexes and extends the knee. Two fibrocartilagenous discs (i.e.,menisci) lie between the tibial and femoral condyles to compensate forthe incongruence of the articulating bones. Because the distal end ofthe femur is curved and asymmetric in shape, the knee joint not onlyflexes and extends like a hinge, but it also slides and rotates duringflexion, resulting in a complex motion for the joint.

Knee OA is characterized by the breakdown of the articular cartilagewithin the joint. Over time, the cartilage may wear away entirely,resulting in bone-on-bone contact. Since bones, unlike cartilage, havemany nerve cells, direct bone contact can be very painful to the OAsufferer. In addition to the pain and swelling, the OA sufferer canexperience a progressive loss of mobility at the knee joint. This is dueto loss of the joint space, where the articular cartilage has completelyworn away. OA usually affects the side of the knee closest to the otherknee (called the medial compartment) more often than the outside part(the lateral compartment). A bowlegged posture also places more pressurethan normal on the medial compartment. The added pressure leads to morepain and faster degeneration where the cartilage is being squeezedtogether.

Various medications are often recommended to reduce the swelling andpain of OA. Other treatments such as weight loss, braces, orthotics,steroid injections, and physical therapy may also help alleviate painand restore function. However, since articular cartilage is avascular,or lacks a blood supply, repair and growth of adult cartilage isminimal. If the pain or immobility becomes too severe and othertherapies do not alleviate the symptoms, surgical interventions becomenecessary. In some cases, surgical treatment of OA may be appropriate.Surgeries can range from arthroscopic procedures to clean the joint byremoving loose fragments of cartilage and by smoothening the rough spotson the cartilage to total knee replacement with an artificial knee.

Another surgical treatment for knee OA is proximal tibial osteotomy, aprocedure intended to realign the angles in the lower leg to help shiftpressure from the medial to the lateral side of the knee. The goal is toreduce the pain and delay further degeneration of the medialcompartment.

In proximal tibial osteotomy, the upper (proximal) part of the tibia iscut, and the angle of the joint is changed. This converts the extremityfrom being bowlegged to straight or slightly knock-kneed. By correctingthe joint deformity, pressure is taken off the cartilage. However, aproximal tibial osteotomy is only temporary before a total kneereplacement becomes necessary. The benefits of the operation usuallylast for five to seven years if successful. The advantage to thisapproach is that very active people still have their own knee joint, andonce the bone heals there are no restrictions on activities.

Another connective tissue disorder that occurs in the knee is excessivepatellar compressive force (PCF). In patients suffering frompatellofemoral arthritis, excessive compressive forces on the patellacause pain and lead to cartilage degeneration between the patella andfemur.

Current treatments to relieve the excessive PCF in such patients involvehighly invasive osteotomies to reposition the attachment point of thepatellar tendon on the tibia. One such procedure is the Maquetprocedure, which displaces the tibial tuberosity anteriorly by cuttingaway a portion of the bone and repositioning it with a bone graftinserted thereunder. Moving the attachment point of the patellar tendonanteriorly decreases the overall PCF by changing the moment arm andeffective angle of the force. However, the procedure is highly invasive,involving high surgical morbidity and significant rehabilitation, whichcan be challenging for some patients. Lack of compliance withrehabilitation can also decrease positive outcomes even in initiallysuccessful procedures.

In addition to the Maquet osteotomy, there are other tibial tubercleprocedures like the Fulkerson osteotomy and Elmslie-Trillat osteotomythat also displace the patellar tendon to reduce the compressive forceson the patella. The osteotomies also redistribute the load on thepatella by transferring the load to other regions of the patella. Thesealternative procedures similarly involve relatively high surgicalmorbidity and require significant rehabilitation.

Another example of compromised connective tissue leading to joint painand loss of function is hip dysplasia. The hip joint is the deepest andlargest joint in the body, and is formed between the head of the femurand the acetabulum of the pelvis (see FIG. 27). The primary purpose ofthe hip joint is to support the weight of the body in both static (e.g.,standing) and dynamic (e.g., running and walking) postures.

Hip dysplasia is a congenital or acquired deformation or a misalignmentof the hip joint. The condition can range from barely detectable toseverely malformed or dislocated. Early-age hip dysplasia can often betreated using a Pavlik harness or a Frejka pillow or splint. In olderchildren, the hip abductor and iliopsoas muscles have to be treatedsurgically because they adapt to the dislocated joint position. Hipdysplasia is often cited as causing osteoarthritis (OA) of the hip at acomparatively young age. Dislocated load bearing surfaces lead toincreased and unusual wear. Subsequent treatment with total hiparthroplasty (hip replacement) is complicated by a need for revisionsurgery due to skeletal changes as the body matures.

The current treatment for dysplasia-related pain is femoral neckosteotomy or periacetabular osteotomy. For more advanced cases, a totalhip replacement is the only surgical option. In either case, thetreatment involves extensive surgery with long rehabilitation protocols.There is thus a need for a less invasive, yet effective approach totreatment.

Compromise of connective tissues leading to joint pain and loss offunction are not limited to humans. For example, the high frequency ofcanine hip dysplasia has made the canine hip a focus of attention amongveterinary orthopedists. Canine hip dysplasia usually begins to manifestitself through decreased activity with varying degrees of joint pain.Often these signs are first observed between the ages of four months andone year.

In a normal canine hip joint, the head of the femur fits congruentlyinto the acetabulum (see FIGS. 61A-B). In a dysplastic joint, thefemoral head conforms poorly to the acetabulum. More space is evidentbetween the bones. Displacement of the femoral head is the hallmark ofthe disease. As with human joint misalignment conditions, varioussurgical procedures—femoral head ostectomy, intertrochanteric osteotomy(ITO), triple pelvic osteotomy (TPO) and total hip replacement, havebeen devised to treat hip dysplasia. There is thus also a need for lessinvasive solutions to joint misalignment conditions and disease forcanine and other veterinary applications.

Given the long-term ineffectiveness of current non-surgical treatmentsand the significant trauma of current surgical treatments, alternativeswith significantly lower surgical morbidity and rehabilitationrequirements could be beneficial to patients showing early as well asadvanced symptoms of compromised connective tissue-related disorders ofarticular joints, such as hip dysplasia, and lateral knee and patellarfemoral osteoarthritis.

SUMMARY OF THE DISCLOSURE

Selectively placed implants are used to address pathologies of jointsarising from improper force distribution. By using appropriately sizedand positioned implants as described herein, displacement of targetedconnective and muscle tissues surrounding the joint is accomplished inorder to realign force vectors and/or alter moment arms loading thejoint to achieve therapeutic effects without cutting bone and withminimal cutting of the connective tissues.

Embodiments of the present invention may be applied to virtually anyarticular joint, including but not limited to the knee and hip. Inaddition to the implants and related prosthesis and apparatus described,embodiments of the present invention include methods of treating jointdisorders and methods of installing implants and prostheses for lessinvasive joint treatments.

In one exemplary embodiment of the invention, an apparatus for treatingan articular joint to effect force distribution in the joint isdisclosed. The exemplary apparatus is for treating articular jointsincluding at least first and second bones with facing articularsurfaces, wherein the bones are positioned with respect to one anotherby associated muscle and connective tissues. These tissues comprisetarget tissues for therapy with the apparatus. Such an exemplaryapparatus may comprise a bearing member with a bearing surface disposedon the bearing member. The bearing member is configured and dimensionedfor placement in a therapeutic location proximate at least one saidtarget tissue and has a thickness sufficient to displace the targettissue from its natural path to a therapeutic path when placed in thetherapeutic location. The bearing surface disposed on the bearing memberis configured to atruamatically engage the target tissue and to permitmovement of the target tissue there along. Specific structures,configurations, dimensions and fixation modalities are described in moredetail herein below.

In another exemplary embodiment of the present invention, a method oftreating an articular joint to effect force distribution in the joint isdisclosed. The exemplary method is suited for treating articular jointsincluding at least first and second bones with facing articularsurfaces, wherein the bones being positioned with respect to one anotherby associated muscle and connective tissues. The exemplary methodcomprises selecting at least one of the associated muscle and connectivetissues as target tissue for treatment, displacing the target tissuewithout severing the bones or target tissue, and redistributing loadingin the joint to achieve a therapeutic effect by the displacement.Alternative and more specific methodologies are described in more detailherein below.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, the drawings show aspectsof one or more exemplary embodiments of the invention. However, itshould be understood that the present invention is not limited to theprecise arrangements and instrumentalities shown in the drawings,wherein:

FIG. 1 is a partially cut away, lateral view of a knee, illustratingconnective tissues and muscles associated with the knee and schematicexamples of implants according to embodiments of the present invention.

FIG. 2 is a partially cut away, posterior view of the right knee,illustrating connective tissues and muscles associated with the knee andschematic examples of implants according to further embodiments of thepresent invention.

FIG. 3 is a front or anterior view of the bones of the right knee joint.

FIG. 4 is a schematic diagram illustrating the human gait cycle, kneejoint moment and flexion angles within the gait cycle, and including asequence diagram illustrating the position of connective tissue throughthe gait cycle with respect to an exemplary embodiment of the presentinvention.

FIG. 5 is a free body diagram illustrating the forces acting on a normalknee joint during a portion of the gait cycle.

FIG. 6 is a free body diagram illustrating forces acting on a knee jointwith excessive medial loading.

FIG. 7 is a free body diagram illustrating forces acting on a knee jointwith an implant according to an exemplary embodiment of the presentinvention.

FIGS. 8 and 8A are a perspective view and a cross-sectional view,respectively, of a soft compliant prosthesis according to an exemplaryembodiment of the present invention.

FIG. 9 is a schematic anterior view of the distal end of a femur with aprosthesis implanted according to an exemplary embodiment of the presentinvention.

FIG. 10 is a schematic anterior view of the distal end of a femur with aprosthesis implanted according to an alternative exemplary embodiment ofthe present invention.

FIGS. 11, 12, 13, 13A and 13B are plan views of prostheses according toalternative exemplary embodiments of the present invention.

FIG. 14 is a cross-sectional view through line 14-14 of FIG. 11 showinga bearing/displacement portion of a prosthesis according to anotherexemplary embodiment of the present invention.

FIG. 15 is an anterior view of a right knee joint with a prosthesisaccording to an exemplary embodiment of the invention implanted thereon.

FIGS. 16, 17, 17A, 18 and 19 are schematic side views and a detailedview of further alternative embodiments of the present inventionincorporating adjustable bearing members.

FIG. 20 is an anterior view of a human knee illustrating positioning ofanother exemplary embodiment of the present invention for addressinglateral force distribution in the knee.

FIG. 21 is a view of a knee joint with a joint spanning prosthesisaccording to another exemplary embodiment of the present invention.

FIG. 22 is a free body diagram of a human knee joint during stairclimbing.

FIG. 23A is a free body diagram of a human knee showing the resultantpatellar compression force in a normal knee.

FIG. 23B is a free body diagram of a human knee showing the modifiedresultant compression force with an exemplary embodiment of the presentinvention.

FIG. 24 is a sagittal section of a human knee with an exemplaryembodiment of the present invention implanted thereon to reduce patellarcompression force.

FIG. 25 is an anterior view of a human knee illustrating the exemplaryembodiment of FIG. 24 as disposed under connective tissues.

FIG. 26 is an anterior view of a human knee illustrating positioning ofa further exemplary embodiment of the present invention for addressingboth lateral force distribution and patellar compressive force asdisposed under connective tissues.

FIG. 27 is a front view of a right side of a hip, showing connection ofthe hip to the femur, and with ligaments removed to show detail.

FIG. 28 is a posterior view of the hip of FIG. 27, with ligaments inplace.

FIG. 29 is a posterior view of a hip showing gluteal muscles, andspecifically the gluteus maximus and the gluteus medius.

FIG. 30 is a posterior view of the hip of FIG. 29, showing lower musclesof the right hip joint.

FIG. 31 is a diagram representing forces exerted on a hip joint.

FIGS. 32A, 32B and 32C are diagrams showing the effect of femoral angleon forces exerted on a hip joint.

FIGS. 33A and 33B are diagrams representing a cross-section of a hipjoint with a prosthesis installed therein in accordance with anexemplary embodiment of the present invention.

FIGS. 34A and 34B are force diagrams showing the effect of theprosthesis of FIGS. 33A-B on the hip abductor force in accordance withan exemplary embodiment of the present invention.

FIG. 35 shows a prosthesis that anchors to the femur and the pelvis inaccordance with an exemplary embodiment of the present invention.

FIG. 36 shows a prosthesis including two tabs for a femur side of theprosthesis in accordance with an exemplary embodiment of the presentinvention.

FIG. 37 shows an exemplary prosthesis, similar to the prosthesis in FIG.36, but not having anchor structures.

FIG. 38 shows an anterior view example of a prosthesis installed in ahip joint in accordance with another exemplary embodiment of the presentinvention.

FIG. 39 is a representation of the prosthesis of FIG. 38, with theligaments and the abductor muscles removed.

FIG. 40 shows a dog bone-shaped prosthesis extending transverse to afemoral neck in accordance with a further exemplary embodiment.

FIG. 41 shows a kidney-shaped prosthesis that extends transverse to afemoral neck in accordance with an embodiment.

FIG. 42 shows a prosthesis mounted on a U-shaped bracket that extendsaround a femoral neck in accordance with an exemplary embodiment of thepresent invention.

FIG. 43 shows a prosthesis mounted as a cap on the greater trochanter inaccordance with another exemplary embodiment of the present invention.

FIG. 44 shows a prosthesis including a groove or channel for receivingthe hip abductor muscles in accordance with an exemplary embodiment ofthe present invention.

FIG. 45 shows a prosthesis including external rollers for permitting hipabductor muscles to roll over the prosthesis as the femur moves inaccordance with an exemplary embodiment of the present invention.

FIGS. 46, 47, 48 and 49 show another example of a prosthesis whichincludes two legs connected by a hinge.

FIG. 50 shows a prosthesis having two hinged elements, each having firstand second crescent moon-shaped legs connected by a hinge, with the twohinged elements nested together in accordance with a further exemplaryembodiment of the present invention.

FIG. 51 shows the prosthesis of FIG. 50 installed on a greatertrochanter.

FIG. 52 shows a strap extending around the femoral neck and the hipabductor muscles in accordance with an exemplary embodiment of thepresent invention.

FIGS. 53, 54, 55 and 56 show examples of cinching mechanisms that may beused for the strap of FIG. 52 in accordance with exemplary embodimentsof the present invention.

FIG. 57 shows an alternative attachment of a prosthesis in which theprosthesis is connected to hip abductor muscles via a band.

FIG. 58 is an anterior view of a human hip with an alternative implantmounted according to an alternative embodiment of the present invention.

FIG. 59 is a lateral view of the embodiment shown in FIG. 58.

FIG. 60 is a side view of the implant shown in FIGS. 58 and 59.

FIGS. 61A and 61B are lateral and anterior views, respectively, of acanine right hind limb and hip.

FIG. 62 is a diagram illustrating vertical force exerted at the caninehip during normal gait.

FIG. 63 is a diagram illustrating relative orientation of the femur andpelvis at the stance phase of the gait cycle in a canine hind limb.

FIG. 64 is a free body diagram illustrating static forces and momentsapplied in canine hind hip joint in a three-legged stance.

FIG. 65 is an anterior view of a canine hip including an implantaccording to an exemplary embodiment of the present invention.

FIG. 66 is a free body diagram illustrating the modification of thebiomechanics of the canine hip joint including an implant according toembodiments of the present invention.

FIG. 67 is a simplified flow chart showing a treatment regimen inaccordance with an exemplary embodiment of the present invention.

FIG. 68 is plot of medial load reduction as determined through acomputer simulation of one embodiment of the present invention.

FIG. 69 is a plot of medial force as determined through a computersimulation of an embodiment of the present invention.

DETAILED DESCRIPTION

Joint conditions that result from or exacerbate unbalanced forcedistribution through the joint may be addressed in embodiments of thepresent invention by interventional techniques involving aredistribution of forces exerted on the joint without the need forhighly invasive surgeries requiring significant trauma to the joint andassociated muscle and connective tissues. In some embodiments of theinvention, increased forces can be selectively applied to one side of ajoint by forcing select muscle and/or connective tissues (targettissues) around a longer or more angled path, thus increasing themagnitude, altering the effective direction, and/or changing the momentarm of forces exerted by such muscles or tissues on the joint. This maybe accomplished, for example, by appropriately shaped implants that maybe placed under selected target tissues relatively non-invasivelycompared to current surgical techniques for addressing such conditions.

In one more specific example of an embodiment of the invention, withparticular application to the knee joint, it is proposed that by placingone or more implants under select target tissues, the lever throughwhich muscle forces act on the joint can be altered to positively affectthe joint loading. With respect to osteoarthritis of the knee, suchtarget tissues may include the muscles, tendons or ligaments of thelateral side of the joint that counter medial forces and alleviateexcessive medial side joint surface contact. As schematicallyillustrated in FIGS. 1 and 2, such a prosthesis could be placed belowtarget tissues including but not limited to the biceps femoris tendon(implants 10A and 10B), the iliotibial band or Tensor Fascia latae(implant 10C), lateral quadriceps-patellar tendon (implant not shown),the lateral gastrocnemius (implant not shown), popliteus, or the fibularcollateral ligament (implant 10E) to laterally displace the relevantmuscle/tendon/ligament. Other target tissues may be readily identifiedby treating physicians based on a patient's particular anatomicalstructure and indications to be addressed.

In other exemplary embodiments particularly applicable to the hip, aprosthesis is arranged superficial to the hip capsule but under at leasta portion of the hip abductor muscle complex to alter the force vectorprovided by the hip abductors. As illustrated for example in FIGS.33A-B, such a prosthesis (implant 220) may be placed or arranged underanyone of, or a combination of multiple, abductor muscles to achieve thedesired resultant force vector. Any of the muscles involved in hipabduction may be targeted, including the gluteus medius GMed, gluteusminimus GMin, the psoas, the piriformis PIR, the tensor fascia latae,the quadratus lumborum, and the rectus femoris. In embodiments, theprosthesis would be placed in the tissue between the gluteus muscles andthe ligaments L, but the prosthesis may be positioned in otherlocations.

Advantageously, the implants according to embodiments of the inventionmay be placed outside the joint capsule so as to minimize interferencewith the function of the joint and the risk of infection and otherproblems associated with the placement of foreign bodies within thejoint capsule. In addition to alleviating the pain and potentiallyaltering the progression of the articular degeneration, placing theprosthesis under the lateral target tissues could also reduce thelateral laxity of the joint. Bursa associated with the target tissuesare likely candidates as locations for such implants and may bedisplaced or removed and replaced by the implants. However preciseplacement at the bursa location is not required and depending on theclinical situation implants according to embodiments of the presentinvention may be placed at sites displaced from associated bursa aswell.

Before addressing more details of exemplary embodiments of the presentinvention, it is helpful to have a basic understanding of the jointbiomechanics, in a first example, the knee. As illustrated in FIG. 3,the knee joint involves four bones, the femur at the top, the fibula andtibia below and patella centrally located at the front. Varus and valgusorientation of the lower extremity (defined as looking at the tibia fromthe knee towards the ankle) are commonly referred to, respectively, asbow-legged (varus) and knock-kneed (valgus).

Because the gait cycle has a critical effect on joint loading, thenormal gait cycle of a human will now be explained with reference toFIG. 4. The gait cycle begins when one foot contacts the ground (A) andends when that foot contacts the ground again (G). Thus, each cyclebegins at initial contact with a stance phase and proceeds through aswing phase until the cycle ends with the limb's next initial contact.(Note that the description of the gait cycle is made with reference tomotion of the black shaded leg in FIG. 4).

Stance phase accounts for approximately 60 percent, and swing phase forapproximately 40 percent, of a single gait cycle. Each gait cycleincludes two periods when both feet are on the ground. The first periodof double limb support begins at initial contact, and lasts for thefirst 10 to 12 percent of the cycle. The second period of double limbsupport occurs in the final 10 to 12 percent of stance phase. As thestance limb prepares to leave the ground, the opposite limb contacts theground and accepts the body's weight. The two periods of double limbsupport account for 20 to 24 percent of the gait cycle's total duration.

When the body weight is borne equally on both feet at rest or in thedouble stance phase of gait (A-B and D-E in FIG. 4), the force thatpasses through the knee is only a fraction of body weight and there isno bending moment around either knee. However, the knee is maximallystressed when body weight passes onto the single leg (B-D).

The resultant forces for a healthy knee in single leg stance are shownin the free body diagram of FIG. 5, wherein x represents the medial(varus) lever arm; y represents the lateral lever arm through which thelateral structures of the knee operate, P represents the weightsupported by the knee, and R represents the resultant joint reactionforce. As a result, the leg has a normal, slightly valgus orientation tothe vertical and the plumb line from the center of gravity falls medialto the center of the knee.

The arrangement of forces exerts a bending moment on the knee actingthrough a medial lever that would tend to open the knee into varus, inother words opening the lateral side of the joint. In standing on oneleg at rest with the knee fully extended, the lateral muscles, tendons,ligaments and capsule are tight. These structures resist the mediallylevered, varus bending moment. In the dynamic situation during gait,multiple muscles which cross the joint in the center or to the lateralside of center combine to provide a lateral resistance to opening of thelateral side of the joint due to the medial lever. These include targettissues such as the quadriceps-patellar tendon, the lateralgastrocnemius, popliteus, biceps and iliotibial tract (see FIGS. 1 and2). The sum of the forces exerted by the target tissue can berepresented as L in FIG. 5, operating through lever arm y. Thiscombination determines the magnitude and direction of the resultantvector R of the tibial femoral joint load. In a healthy knee, thisresultant is approximately centered between the lateral and medialcondyles.

With increasing knee varus angle, the medial lever arm increases,requiring an increased lateral reaction L to prevent the joint frombecoming excessively loaded on the medial side. If the forces urging theknee into a varus state reach a threshold level, as diagrammaticallyillustrated in FIG. 6, the ability of the associated connective tissuesto compensate in their natural state is overcome so that the joint loadR is borne on the medial compartment, leading to excessive wear, andeventually potentially significant joint pain. This situation is acondition that gives rise to osteoarthritis of the knee.

The situation illustrated in FIG. 6 can be addressed according toembodiments of the invention by altering the position of target tissuesacting on the joint in order to adjust one or more of the forcemagnitude, angle and/or moment arm. Thus, as mentioned above, inexemplary embodiments, one or more implants are placed under selectedtarget tissue in order to beneficially alter the force distribution byincreasing the lateral moment (counterclockwise in the figure).

FIG. 7 illustrates an exemplary embodiment of the present invention witha generic implant 10 according to one embodiment positioned along thejoint to assist in redistributing the forces acting on the joint toprovide a therapeutic effect. As shown therein, implant 10 creates aspace adjacent to the joint that forces the target tissues (not shown)that run there along to assume a longer path over the implant surface.That longer path may have a number of beneficial effects, includingincreasing the lateral moment arm y′, moving the line of action for thetarget tissue to a more effective angle and/or tensioning the targettissue to increase amplitude of force vector L′. As a result, theeffective lateral moment is increased to more effectively counter themedial moment created by supported weight P. This moves the joint load Rlaterally out of the medial compartment and back to a more normal,central location. Implant 10 may take many forms as discussed in moredetail below with respect to various exemplary embodiments of thepresent invention.

The amount of displacement of the target tissue need not be large inorder to potentially have a substantial effect on increasing lateraltorque to assist in unloading the medial compartment. For example, anaverage person has a normal lateral lever arm (y) of about 50 mm. Thus,a lateral displacement increasing the lever arm (y′) by only about 10-15mm may increase the lateral torque by about 20%-30%. Dependent upon thegeometry of a particular patient's joint, lateral displacements ofbetween about 5 mm to about 30 mm may be possible, with displacements inthe range of about 10 mm to about 30 mm, or more specifically about10-20 mm, most typical.

EXAMPLE

To evaluate the change in loading in the medial compartment of the kneedue to lateral displacement of the target tissue, simulations wereperformed using a computational model of the knee to determine anapproximate percentage reduction in medial contact force. (For detailsof the computational model, see Lin, Y.-C., Walter, J. P., Banks, S. A.,Pandy, M. G., and Fregly, B. J., Simultaneous Prediction of Muscle andContact Forces in the Knee During Gait, p. 945-952, Journal ofBiomechanics 2010, which is incorporated herein by reference). Medialcontact forces were calculated at the two points of the gait cycle withpeak medial contact forces (approximately 15% and 50% of the gait cycleat peaks 1 and 2, respectively) as a function of lateral displacement oflateral knee muscles. Lateral muscles were displaced 0 to 35 mm inincrements of 5 mm as described in connection with embodiments of theinvention. In this simulation, the origins of the three lateral kneemuscles (tensor fascia latae, biceps femoris long head, and bicepsfemoris short head) were displaced laterally from the femur while therewas no change to the insertion sites of the muscles. The results ofthese simulations, presented graphically in FIG. 68, showed that averagemedial load could be reduced by as much as about 12% at displacement ofabout 35 mm according to embodiments of the invention.

Simulations were also performed for absolute medial contact force as afunction of percent of stance phase with the origin of the lateralmuscles displaced by 30 mm. In this simulation, the origins of the threelateral knee muscles (tensor fascia latae, biceps femoris long head, andbiceps femoris short head) were displaced laterally from the femur whilethere was no change to the insertion sites of the muscles. Results ofthis simulation, represented graphically in FIG. 69, show that medialcontact force is generally reduced over the range of motion byembodiments of the invention simulated. Under the simulated conditions,force reductions in the range of about 100N were achievable at pointswithin the gait cycle. Plot 2 also plots the medial contact forceswithout the implant. The unshifted, generally upper line represents thesimulation run without the implant and the shifted, generally lower linerepresents the simulation run with the implant.

Implants according to embodiments of the present invention may beconfigured and secured in a variety of ways as described below in moredetail with respect to exemplary embodiments. In general, such implantsmay be rigid, semi-rigid or soft compliant prostheses secured toadjacent bone or the surrounding tissues. Implants also may be held inplace by the surrounding tissues without using a fixation element. Softcompliant prostheses could be filled with water, saline, silicone,hydrogels, etc., sufficient to move the tissue laterally as describedabove. Such a soft compliant prosthesis could be placed in a deflatedstate and then inflated to the appropriate thickness. Alternatively,implants may be filled with other flowable materials including beads orother particles made of metal, polymer, or foam material, optionally ina liquid medium, which conform to the adjacent bone or tissue surfaces.Thixotropic materials, such as hydrogels derived from hyaluronic acid,change their mechanical properties as shear stress is applied to them.An implant filled with such materials could be made to change the amountof lateral displacement that it provides based on the shear stress thatit sees from overlying target tissues at various points in the gaitcycle. Implants may be coated with materials to reduce friction such ashydrophilic coatings or polytetrafluoroethylene (PTFE) coatings.Additionally or alternatively, the prosthesis may be adjustable to allowthe dimensions such as thickness of the prosthesis to be adjusted duringsurgery or anytime after surgery. Rigid or substantially rigidprostheses could be made of known bone-compatible implant materials suchas titanium or stainless steel. Whether rigid or compliant the surfaceof the prosthesis should be designed to minimize negative effects ofmovement of the connective tissues thereacross. Such prosthesis could beimplanted arthroscopically or using a mini-open or open surgicalapproach.

An exemplary embodiment of a soft compliant implant is illustrated inFIG. 8. In this embodiment, implant 20 includes a body member 22 madewholly or partially of a soft compliant material such as describedabove. Body member 22 has an upper (laterally-facing) bearing surface 21configured to slidingly engage the target tissue to be displaced.Bearing surface 21 thus forms a displacement portion of the implant. Thebearing surface is preferably made or coated with a lubricious materialsuch as PTFE or a hydrophilic material to reduce friction with thetarget tissue. Body member 22 is further shaped to enhance its abilityto stay in the desired position with respect to the target tissue. Inthis regard, body member 22 has a generally hour glass-like shape with athinner and narrower central section 24 and wider and thicker endsections 26 to follow the contours of the target tissues. Preferably,body member 22 is shaped such that upper bearing surface 21 forms alongitudinal trough or channel which guides and retains the targettissue on the bearing surface as it slides relative thereto.Accordingly, body member 22 may have greater thickness along its lateraledges than along its middle, or the lateral edges may be curved or bentupward to inhibit the target tissue from sliding off the edges of bodymember 22. Body member 22 is preferably shaped so as to slip under thetarget tissue and be self-retained in position due to compressionbetween and friction with the adjacent tissues, without need forseparate fasteners. Optionally, the lower side (opposite the upperbearing surface) may have friction-enhancing features such as bumps,scales, or projections which engage the underlying tissue to enhanceretention, thus forming a fixation portion. As a further option, inorder to further secure the implant in the desired location, attachmentmeans such as holes 28 for fasteners such as sutures or straps may beprovided on either or both ends of body member 22, or a flexible strapor band 29 configured to be wrapped around the target tissue may becoupled to or integrally formed with either the superior or inferiorends of body member 22. In one exemplary embodiment, an implantgenerally configured in the manner of implant 20 may be well suited forinsertion under the iliotibial tract.

In another exemplary embodiment of the invention, as shown in FIG. 9,prosthesis 30 provides lateral displacement by inserting a passive,space-occupying implant under the target tissue as described above.Prosthesis 30 comprises a body member 32 that defines displacementportion 33 and fixation portion 34. Displacement portion 33 is theportion responsible for displacing the target tissues as required toaccomplish the force redistribution. The medial surface of displacementportion 33 is preferably shaped to conform to the external shape of thelateral femoral condyle and may have a hook- or spoon-like shape on itsdistal end to wrap partially around the distal facet of the lateralfemoral condyle. Displacement portion 33 is preferably rounded andsmooth on its lateral side to provide a smooth surface over which thedisplaced soft tissues may slide. Fixation portion 34 is shaped so thatit lies more flat under the muscles and tendons higher up the femur,away from the complexity of the areas adjacent to the femoral condyles,where many different tissues crossover and attachments to bone canoccur. This more cranial segment of the femur would allow easier accessto the underlying bone and potentially better fixation. Fixation couldbe achieved by any known means for bone-secured implants, such as bonescrews 36, tacks, anchors or adhesives, to name a few possibilities. Theimplant could be made from any suitable material, either hard or softmaterials. In this case, silicones of varying grades and durometers,titanium, stainless steel or pyrolytic carbon are examples of materialswhich would be appropriate choices.

In one alternative embodiment, depending on specific patient conditions,it may be desirable to directly secure the prosthesis to the femur inthe condyle region. Prosthesis 40, shown in FIG. 10, illustrates anexample of such a prosthesis. In this embodiment, the fixation anddisplacement portions are collocated within body member 42 closer to thecondyles of the femur. The configuration of the body member with respectto its displacement function would be essentially the same as describedabove. Fixation would also be substantially as previously described, forexamples screws 44 are illustrated, except that it is adapted to allowfixation and displacement functions to be collocated.

In various alternative embodiments, the displacement portion and thefixation portion of prostheses according to the invention may be ofunibody construction, or may be formed of two or more parts depending ondesired function. For example, the fixation portion may be stainlesssteel or titanium textured to enhance bony ingrowth and solid screwfixation, while the bearing/displacement portion could be made of adifferent material, for example, pyrolytic carbon to enhance the abilityof overlying tissues to slide across the implant, or PTFE, silicone orother low-friction polymer with suitable wear characteristics to providea softer bearing surface. In further alternatives, the displacementportion could be comprised of a substrate of one material with anoverlying layer forming the bearing material. The substrate could beeither attached to or contiguous with the fixation portion.

The fixation and displacement portions may be in-line with one another,or they may be offset from one another, or a combination of both withmultiple displacement portions. Alternative exemplary embodiments inthis regard are illustrated in FIGS. 11-13B. For example, prosthesis 50in FIG. 11 includes a base member 52 that is configured to positiondisplacement portion 53 anteriorly with respect to fixation portion 54.Base member 52 thus has a generally straight section configured to bemounted to the femur and a curved section that extends anteriorly fromthe straight section when implanted. Displacement portion 53 is attachedto the curved section and extends inferiorly so as to be positionedbeneath the target tissues adjacent the lateral femoral condyle. In thisembodiment, displacement portion 53 may have on either or both themedial and lateral surfaces thereof a bearing surface 56 of a differentlower friction material than that of the remainder of the bearingportion 53. Alternatively, base member 52, the displacement portion 53,and/or the bearing surface 56 may be the same material, and may be ofunibody construction. Fixation holes 58 are provided in the fixationportion to receive screws for attachment to the bone.

Prosthesis 60 provides another exemplary embodiment, shown in FIG. 12,which includes base member 62 having a spanning section 61 betweendisplacement portion 63 and fixation portion 64. Once again, fixationholes 68 are provided as one alternative fixation means, and a separatebearing surface 66 may be provided. Alternatively, base member 62 andthe displacement portion 63 may be the same material, and may be ofunibody construction. In this embodiment, spanning section 61 extendsgenerally vertically between the fixation portion 64 and displacementportion 63 and is offset posteriorly with respect to both the fixationportion 64 and displacement portion 63 in order to avoid criticalanatomical features adjacent the joint. Depending on specific jointanatomy and patient conditions, the spanning section may be designed topermit secure fixation at a suitable site while still placing thedisplacement portion under the target tissue while minimizing trauma toimportant intervening tissues.

In yet another exemplary embodiment, multiple displacement portions maybe provided as shown in FIG. 13. For example, prosthesis 70 includesbase member 72 that defines anterior displacement portion 73A andposterior displacement portion 73B. These are joined by spanning section71 to fixation zone 74 where fixation holes 78 are located. In thisembodiment, each of displacement portions 73A and 73B includes a bearingsurface 76. Again, the bearing surface may be integral, or attached tothe base members. Further, in this or any other embodiment herein, thedisplacement portions 73A, 73B may be movably coupled to the spanningsection 71 or fixation zone 74 by means of a rotatable or slidablecoupling 75, for example as shown in FIG. 13A, thereby being movablewith joint motion. Alternatively, spanning section 71 or the jointsbetween it and the displacement portions may include flexible portions77 so as to deflect in response to joint movement, as shown in FIG. 13B.In a further alternative, the flexible portion 77 may be malleable toallow the surgeon to deform and/or reposition displacement portions 73A,73B to a desired configuration before or after the prosthesis has beenfastened in place. As yet another alternative, the couplings between thedisplacement portions and the spanning section 71, or between thespanning section and the base member 72, may be movably adjustable toallow the surgeon to position the components in various locationsrelative to one another and fix them in any such position.

As illustrated above, the displacement portion of prostheses accordingto embodiments of the present invention may have any number of differentshapes as desired to cooperate with specific target tissues as neededfor the pathology of a given patient. In further examples, more complexgeometries may be provided in order to vary the target tissuedisplacement in coordination with the patient gait cycle and loadingconditions created throughout the cycle. For example, the bearingsurface may be configured to provide relatively little tissuedisplacement and force realignment as the knee is flexed through thegait cycle, but to deflect the target tissues more as the knee isextended fully during the gait cycle, providing the necessary correctionappropriate for that pathology. This feature can be achieved byoptimizing implant static geometry, by enabling dynamic changes inimplant position or geometry depending upon joint position or loading,or as previously mentioned, by selection of certain implant materials.For instance, the outer shell of an implant could be a resilientmaterial such as silicon, filled with a thixotropic fluid. During thegait cycle, the shear stress exerted on the implant causes the viscosityof the thixotropic filler to drop, allowing the fluid to flow to thesides of the implant, and causing less displacement. As the knee isextended fully in the stance phase of the gait cycle, the resilientshell of the implant urges the thixotropic fluid back into its originalposition, whereupon the viscosity increases again to provide greaterdisplacement.

One exemplary embodiment showing the more complex geometry referred toabove is shown in FIG. 4, which was referred to previously in theexplanation of the gait cycle. Shown at the bottom of FIG. 4 is atransverse cross-section through the displacement portion 83 of anexemplary prosthesis, which may have an overall configuration such as,for example, the configuration of prosthesis 60 in FIG. 12. In otherwords, displacement portion 83 in FIG. 4 is viewed from a cranial aspecttowards the caudal aspect. Bearing surface 86 provides a ramped surfacewith lesser thickness dorsally, increasing in the ventral direction. Thebearing surface is thus configured such that during the gait cycle thedisplaced target tissues T slide ventrally and dorsally there along. Asshown in the first graph of FIG. 4, the adduction moment acting mediallyon the knee occurs during the stance phase when leg is loaded. Duringthis phase, the joint angle is generally in the range of about 0° toabout 20°, with the greatest forces being applied when the knee isstraight or close to straight. Thus, to provide maximum effect, bearingsurface 86 is configured so that target tissue (T) is at an area ofmaximum displacement when the joint angle is in the range of about0°-10°, lesser displacement at an area where the target tissue (T)resides at joint angles in the range of about 10°-20° and minimaldisplacement when the joint angle exceeds about 20°.

The geometry shown for displacement portion 83 in FIG. 4 is idealizedfor the gait cycle when walking on a flat surface. In reality, walkingoccurs on uneven ground and up and down stairs, which can causesubstantial loading on the knee at joint angles greater than about 20°,such angles usually being less than about 60°, but in most cases not atangles greater than about 90°. Thus specific geometries for the bearingportion may need to be designed with particular patient needs in mind.

Another complex geometry is shown in FIG. 14. In this alternativeembodiment, displacement portion 53 of prosthesis 50 (FIG. 11) isprovided with bearing surface 56 having grooves 57, or other variationsof the bearing surface geometry to fit the anatomical track and motionof the target tissue as the joint moves through the gait cycle, thusoptimizing the force distribution created by the prosthesis at eachjoint position.

FIG. 15 illustrates an exemplary implantation of a prosthesis accordingto the present invention, in this case implant 60 shown above in FIG.12. In this example, implant 60 is used to displace the fibularcollateral ligament. A similar implant and positioning is depicted asimplant 10E in FIG. 2. In other instances, the implant may be configuredto displace other muscles or tendons such as the biceps femoris tendon(as positioned by implant 10B in FIG. 2) or the iliotibial band. Withreference again to FIG. 15, fixation portion 64 of implant 60 isattached to the femur so that base member 62, including displacementportion 63, extends caudally beyond the end of the femur to at leastpartway across the joint space. With spanning section 61 posteriorlypositioned, the device is shaped to jog around the attachment point(s)of surrounding tissues (including potentially the target tissues) andallow fixation portion 64 to be situated above the attachment area onthe femur. More specifically, spanning section 61 circumvents theattachment sites of the plantaris muscle and the lateral head of thegastrocnemius muscle. Both the plantaris muscle and the lateral head ofthe gastrocnemius muscle attach to the posterior of the lateral femur.By having a posteriorly offset spanning section 61, the implant avoidsthese attachment sites and allows the bearing surface 66 (see FIG. 12)to laterally displace the collateral ligament. Once again, displacementportion 63 may be shaped so that target tissue (T) track is displaced ata position such that contraction forces of the target tissue (T) arepredominantly in the direction normal to the bearing surface of thejoint, such that minimal or no moment arm and torsion is created. Thiswill help to reduce or prevent any undesired forces onto or micromotionof the device, which could result in loosening of the fixation of thedevice over time.

In other exemplary embodiments of the invention, shown in FIGS. 16-19,prostheses according to the invention are adjustable to increase ordecrease the amount of displacement exerted on the target tissues eitherduring implantation or post surgery via a simple percutaneous access.For example, prosthesis 100, shown in FIG. 16, includes a base member102 with a moveable bearing member 110 mounted within the displacementportion 103. Fixation portion 104 extends superiorly from thedisplacement portion for fixation to the femur substantially aspreviously described. Bearing member 110 has an outer bearing surface106 also substantially as previously described. Bearing member 110 maybe secured to base member 102 by adjustment means such as screw 112 andalignment posts 114. Other suitable adjustment means, such as ratchetingposts, sliding posts with separate locking means or other means forproviding the adjustment, may be applied by persons of ordinary skill inthe art. Access port 116 through bearing surface 106 allows access of atool to rotate screw 112 to adjust the bearing member in (medially) orout (laterally) with respect to the base member, thus adjusting themagnitude of displacement of the target tissue. Persons of ordinaryskill in the art will also appreciate that any of the adjustabilityfeatures described herein may be incorporated with any of the geometriesdescribed above.

Prosthesis 120 in FIG. 17 illustrates another exemplary embodiment,including a base member 122 with bearing members 130, 131 adjustablyattached in displacement portion 123. While this exemplary embodimentincludes two adjustable bearing members, persons of ordinary skill inthe art will appreciate that more parts of the displacement portion maybe provided to accommodate the desired adjustability for the desiredgeometry. In this embodiment, screws 132 are once again used as theadjustment means. However, it will again be appreciated that other meansof adjustment could be provided.

Given the curved shape of the bearing surface 126 and the separateadjustment points, prosthesis 120 includes an expansion joint 134between the two bearing members 130, 131 to accommodate the separationof the bearing members in view of the adjustability feature. While thetwo or more bearing members could simply separate to leave a small gapbetween them as they are adjusted outward from their minimumdisplacement position, it may be desirable to provide a relativelysmooth, relatively contiguous bearing surface 126 as the adjustment anddisplacement is increased. As shown in FIG. 17A, interlaced fingers 137of expansion joint 134 help prevent the formation of large gaps thatcould pinch or grab the target tissue as it moves across the bearingsurface. Alternatively, the bearing surfaces of bearing members 130, 131could be covered with a single membrane of suitably elastic low-frictionmaterial extending across the gap between the members which couldresiliently expand or contract with adjustments in position of thebearing members.

In a further exemplary embodiment, prosthesis 120′ in FIG. 18 issubstantially the same as prosthesis 120 described above except for theconfiguration of expansion joint 134. In this exemplary embodiment,rather than interlaced fingers, expansion joint 134 utilizes bearingmembers 130, 131 with overlapping tapered ends 138, 139, respectively,which slide relative to one another to form a smooth bearing surface 126free of gaps providing a smooth overlapped expansion zone.

In a further alternative embodiment, prosthesis 140 provides anadjustment mechanism that is accessed from the anterior and/or posterior(A/P) aspect of the knee, as shown in FIG. 19. In this embodiment, basemember 142 has two alignment posts 154 that extend from the displacementportion 143. Bearing member 150 receives the alignment posts. One ormore slideable wedge members 152 are disposed between the bearing member150 and base member 142 between posts 154 and are movable posteriorlyand anteriorly relative to base member 142 and bearing member 150.Actuating screws 151 or other adjustment devices move the wedges in andout underneath the bearing surface, which slides the bearing surfacemore or less laterally relative to the base member, thereby adjustingthe displacement of the target tissues.

In various adjustable embodiments described above, the adjustment screwsthemselves may be radiopaque and/or otherwise discernable from the restof the implant under x-ray in order to enable post-surgical percutaneousadjustment of the device. Alternatively, target features can be builtinto the device to locate the adjustment points without having thescrews or adjustment means themselves radiopaque, such as radiopaquerings or markers built into the nearing surface of the device itself.

In still further alternative embodiments, the bearing members ofembodiments described herein may be movable by means of an inflatablebladder disposed between the bearing member and the base member. Thebladder may be filled with a liquid or gas under suitable pressure toallow adjustment of the bearing member position and associateddisplacement of the target tissue. The bladder will have an inflationport for introduction of inflation fluid by means of an inflationdevice, which may be similar to the inflation devices used for inflationof angioplasty balloons.

Devices described above generally disclose placement of a device on thefemoral side of the femoral patellar joint. Devices in accordance withembodiments of the invention may also be placed on the tibial side tolaterally displace the target tissues by being fixed on the tibia or thefibula. An exemplary tibially-fixed implant is shown in FIG. 20.

Referring to FIG. 20, implant 154 is inserted underneath the iliotibialband (IT) just superior to Gerdy's tubercle, to move the iliotibial bandlaterally and/or anteriorly. Implant 154 includes a displacement portion155, spanning section 156 and fixation portion 157 as previouslydescribed. Bone screws 159 may be placed through holes in the fixationportion to secure the implant to the tibia. Other fixation means asdescribed herein may be alternatively employed. Implant 154 may bepositioned as shown to rebalance dynamic loading on the knee joint in alateral and/or anterior direction. It may reduce symptoms andprogression of medial osteoarthritis in the knee. It may also improvethe strength and stability of the knee, by giving the muscles which acton the iliotibial band greater leverage. It will be understood thatimplant 154 may also be configured to displace muscles, tendons, ortissues other than the iliotibial band, including the biceps femorisshort head, biceps femoris or fibular collateral ligament, among others.

A further advantage of implant 154, positioned as shown, may be toreduce the incidence and/or severity of Iliotibial Band Syndrome.Iliotibial. Band Syndrome, or Iliotibial Band Friction Syndrome,typically occurs because the iliotibial band is rubbing against thelateral femoral epicondyle, the femur or other tissues on the lateralside. Thus, embodiments of the invention also may be used for treatmentof conditions involving excessive friction or pressure between tissuesin the knee or other joints, alone or in combination with osteoarthritistreatment. By moving the iliotibial band laterally and/or anteriorly,the pressure of the iliotibial band against these tissues may berelieved.

For placement of implant 154, surgical dissection of the iliotibial bandcould be made from the posterolateral edge or the anteromedial edge ofthe iliotibial band. However, it may be preferable to make thisdissection from the anterolateral edge, between Gerdy's tubercle and thetibial tuberosity. Fixation portion 157 could then be attached to thetibia underneath the muscle which runs between these two tuberosities.

It will be understood that while many embodiments described herein aredescribed as being secured to only one of the two bones associated witha joint, embodiments also may be secured to both of the bones. Forexample, in the case of the knee, to both femur and tibia or femur andfibula. In another exemplary embodiment, shown in FIG. 21, prosthesis160 spans the entire joint and is fixed to both the femur and either thetibia or fibula, depending on geometry. Prosthesis 160 is provided witha sliding hinge 174 or other suitable articulated joint to allow freedomof movement of the joint. More specifically, in this exemplaryembodiment, base member 162 includes upper and lower fixation portions164 with displacement portion 163 disposed between and including slidinghinge 174. Displacement of the target tissues is once again provided bybearing surface 166 across which the target tissue tracks. The bearingsurface may be made adjustable by providing a separate bearing memberand adjustment mechanism as described above. Displacement may also becontrolled by an additional or alternative displacement means as shownin FIG. 21. In this embodiment, one or more expansion members 172 aredeployed under base member 162. Expansion member 172 may comprise aninflatable device such as a balloon or a mechanical adjustment such as ascrew mechanism. The expandable member(s) 172 may be positioned so as toexert force on only the femur or only on the tibia or fibula, orpositioned more centrally along the joint to exert force on both femurand tibia. The sliding members making up the displacement portion 163,or the regions where these members join to the upper and lower fixationportions 164, may be flexible so that the bearing displacement portion163 is deflectable laterally with expansion of expansion members 172,thereby increasing the displacement of target tissues.

In other embodiments of the invention, joint disorders related to forcesin other planes such as the lateral plane may be addressed. Thebiomechanics of the knee in the coronal or frontal plane have beendescribed above, with a variety of embodiments generally in amedial/lateral direction to address imbalanced loads at the interface ofthe femoral and tibial articular surfaces. Looking at the knee in thelateral plane, there is a different set of force components that actanteriorly and posteriorly, resulting in loading between the patella andfemur.

With reference to the free body diagram in FIG. 22, the two main momentsacting around the knee joint are due to the ground reaction force W andthe patellar tendon force F_(p). The flexing moment on the lower leg isthe product of the ground reaction force (W) and the perpendiculardistance of the force from the center of motion of the knee joint, (a).The counterbalancing extending moment is the product of the quadricepsmuscle force acting through the patellar tendon and its lever arm, (b).Hence, for a given individual, the magnitude of the patellar tendonforce F_(p), can be calculated as F_(p)=Wa/b.

The action of the quadriceps muscle and the patellar tendon on thepatella during flexion/extension results in a patellar compression force(PCF), as shown in FIG. 23A. The resultant (R) PCF is dependent on themagnitude of P and its effective angle of action (β).

Referring to FIG. 23B, resultant force R′ is decreased by positioningimplant 200 under the patellar tendon, thus displacing it anteriorly toincrease the lever arm b (FIG. 22), thereby reducing the patellar tendonforce F_(p), and increasing the effective angle of action β′, therebyreducing the horizontal component of the patellar tendon forcecorresponding to the PCF. The resultant PCF (R′) is thus reduced,lessening the force with which the patella is pressed against the femur.

Anticipated advantages of this embodiment of the present inventioninclude a reduction in the rate of cartilage degeneration and/or pain inthis area. An implant such as implant 200 may be configured toredistribute the point of highest load between the patella and femursuperiorly, caudally, laterally or medially so as to reduce the stresson any specific area of that interface. It should also increase themoment arm of the muscles acting on the patellar tendon, therebyproviding greater effective strength and stability to the knee, andlowering the total load on the knee joint.

One exemplary embodiment is illustrated in FIGS. 24 and 25, which showimplant 210 placed on the tibia to displace the patellar tendon withoutcutting the tibial tubercle or severing any of the connective tissues asdescribed above. As with other embodiments described herein, implant 210comprises support member 212 and bearing member 214, which in this caseare integrally formed but may be separate components as elsewheredescribed herein. The support and bearing members are functionallydivided into displacement portion 216, which engages and displaces thepatellar tendon, spanning section 218 and fixation portion 220. Fixationportion 220 includes means for securing the implant as described herein.In this exemplary embodiment, holes are provided for bone screws 222 inorder to fix the implant against the tibia.

As illustrated in FIG. 25, implant 210 may be inserted from the lateralside of the patellar tendon. It could also be inserted from the medialside. Implant 210 is configured such that fixation portion 220 lies inan area that does not have tendon insertions or other connective tissueattachment points. The configuration also may permit displacementportion 216 to rest against the tibia just cranial to the tibialtubercle and just caudal to the knee capsule. Such positioning willtransfer any load directly to the tibia below the implant, therebyminimizing the stresses on the rest of the implant and the tibia itself.

The inner surface of fixation portion 220 that rests against the tibia,as with other embodiments described herein, may be designed andmanufactured with the appropriate materials and textures to encourageingrowth of bone into the implant, to provide more support and preventmotion of the implant relative to the bone surface to which it issecured; in this case the tibia. Spanning section 218 should be designedto experience relatively low stresses, and may therefore be fairly thin,to avoid creating an irritating or unsightly bump. Round, channeled,box-shaped, curved or other cross-sectional geometries may be selectedto enhance bending stiffness or torsional rigidity as needed forspanning section 218. Again, spanning section 218 should not interferewith any of the muscle insertion points in the area of the tibialtubercle.

Displacement portion 216 is configured and dimensioned to avoid the kneecapsule and to avoid interfering with the patella, even when the leg isextended. It should also be designed to minimize any additional stresson the patellar tendon itself. Therefore the bearing surface ofdisplacement portion 216, against which the patellar tendon rests, mayhave a curved ramped shape as best seen in FIG. 24. This bearing surfacemay be hard and smooth, made from materials such as polished pyrolyticcarbon, steel, or titanium, or coated or covered with a lubriciousmaterial, such as PTFE. It might alternatively be designed to encourageadhesion and ingrowth of the patellar tendon onto this surface, so thatthe implant acts even more as an extension of the tibial tubercle. Forexample the surface may be porous, roughened, or configured withopenings into which bone or scar tissue may grow to enhance adhesion.

The precise positioning of the patellar tendon accomplished with implant210 will depend upon the particular clinical situation. As will beappreciated by persons of ordinary skill in the art, such implants maybe designed to move the patellar tendon anteriorly or medially oranterior-medially. This may be accomplished by making one side (lateralor medial) of the displacement surface higher than the other, and/or byforming a track with ridges on one or both sides of the bearing surfaceto urge the patellar tendon in a lateral or medial direction.

Implants such as implant 210 may be inserted in a relatively quickprocedure with low morbidity. A relatively short incision could be madeto one side of the tibial tubercle. From this incision a probe could beused to tunnel under the patellar tendon and expose the surface of thetibia underneath. The implant could then be inserted into this tunnel,fitted against the tibia, attached to the tibia with the appropriatescrews or other fixation elements as appropriate, and then the incisioncould be closed. Since there is little or no cutting of bone, muscle, ortendon, morbidity should be minimal, and the recovery and rehabilitationafter this procedure should be rapid and involve much less pain whencompared with the existing surgical options.

An implant similar to implant 210 may also be applied in otheranatomical locations. For example, on the anterolateral aspect of thetibia is Gerdy's tubercle, the insertion site of the iliotibial band. Animplant such as implant 154 described above may be positioned in thislocation. Additionally, it may be preferable in some patients todisplace both the patellar tendon and the iliotibial band. This could bedone with two separate implants, such as implants 154 and 210 asdescribed above, or a single implant could be provided.

An example of a single implant for displacing both the patellar tendonand iliotibial band is shown in FIG. 26. In this exemplary embodiment,implant 230 again includes a displacement portion 232 divided into twoparts, iliotibial band displacement portion 232A and patellar tendondisplacement portion 232B. Spanning section 234, formed as describedabove, joint displacement portion 232 to fixation portion 236. Again, avariety of fixation means as described herein may be employed by personsskilled in the art, with bone screws 238 being illustrated in theexemplary embodiment. A single implant such as implant 230 may providegreater strength and stability as compared to the use of two separateimplants such as implants 154 and 210.

In general, materials, alternative configurations and methods related toimplants 210 and 230 may be as described elsewhere herein for otherexemplary embodiments.

As mentioned above, further alternative embodiments of the presentinvention have application in the treatment of disorders of the hip.FIG. 27 illustrates the basic anatomy of a hip joint H. As shown, thehip joint H is the joint between the femur F and the concave cavity ofthe pelvis P, called the “acetabulum” A. The femur F extends upward froma knee of a body, and includes a greater trochanter G at an outer topedge at the juncture of the shaft S of the femur and the femoral neck N.A lower trochanter is located opposite the greater trochanter G, and afemoral head FH is located at the distal end of the femoral neck N. Theconcave-shaped acetabulum A forms at the union of three pelvic bones:the ilium I, the pubis PU and the ischium IS. A blanket of ligaments L(removed in FIG. 27 to show detail; shown in FIG. 28) covers the hipjoint H, forming a capsule and helping to maintain the femoral head FHin the acetabulum A.

A series of muscles extend over the ligaments L and attach between thefemur F and the pelvis P. Included among these muscles are the gluteusmaximus GMax (FIG. 29), the gluteus medius GMed, and the gluteus minimusGMin (FIG. 30). The gluteus maximus GMax is the uppermost of these threemuscles. It is the largest of the gluteal muscles and one of thestrongest muscles in the human body. Its action is to extend andoutwardly rotate the hip, and extend the trunk.

The gluteus medius GMed is a broad, thick, radiating muscle, situated onthe outer surface of the Pelvis P. The gluteus medius GMed starts, ororiginates, on the outer surface of the ilium I. The fibers of themuscle converge into a strong flattened tendon that inserts on thelateral surface of the greater trochanter G.

The gluteus minimus GMin is situated immediately beneath the gluteusmedius GMed. It is fan-shaped, arising from the outer surface of theilium I. The fibers of the muscle end in a tendon which is inserted intoan impression on the anterior border of the greater trochanter G, andgive an expansion to the capsule of the hip joint H.

The gluteus medius GMed is the primary muscle responsible for hipabduction, with the gluteus minimus GMin assisting. Actingsynergistically with these are the psoas, piriformis PIR (FIG. 30),Tensor Fascia Latae (TFL), quadratus lumborum, and rectus femoris. Themain function of the hip abductor muscles is to provide frontal-planestability to the hip in the single-limb support phase of the gait cycle.This is achieved when the hip abductor muscles produce a frontal-planetorque that equals the frontal-plane torque produced by the body weight.

Due to the difference in moment arms of the hip abductor force and bodyweight force, the hip abductor muscles must produce a force twice thebody weight, resulting in compressive joint load of three to four timesbody weight during normal walking. For example, FIG. 31 is a diagramrepresenting forces exerted on a hip joint H. S is the center ofgravity, K is the mass of the body, h′ is the moment arm of the bodyweight K, M is the force exerted by the abductor muscles, h is themoment arm of the abductor muscle force M, and R is the resultantcompressive force transmitted through the hip joint (R is the resultantforce of K and M). As can be seen, the h′ is significantly longer thanh, requiring that the hip abductor force M be substantially more thanthe body weight force K for stability at the hip joint H.

The compressive force vector R transmitted through the hip joint H isaffected by the femoral neck angle since it affects the angle and themoment arm of the abductor muscle force. The angle between thelongitudinal axis of the femoral neck FN and shaft S is called thecaput-collum-diaphyseal angle or CCD angle. Such angle normally measuresapproximately 150° in a newborn and 125-126° in adults (“coxa norma”;FIG. 32A). An abnormally small angle is known as “coxa vara” (FIG. 32B)and an abnormally large angle is known as “coxa valga” (FIG. 32C).

In coxa valga (FIG. 32C), the moment arm h′ of the hip abductor musclesis shorter than the normal hip, resulting in the need for a much higherhip abductor muscle force M. Additionally, the line of action of theabductor muscle force M is closer to vertical, requiring a higher forceto offset the moment arm h of the body. The resultant compressive forceR therefore is larger and is closer to the edge of the acetabulum A,thereby decreasing the weight bearing surface of the acetabulum. Thisabnormal loading of the acetabulum leads to degenerative changes alongthe rim of the acetabulum A, resulting in pain and eventual loss ofarticular cartilage.

In the case of a shallow acetabulum, the resultant force acts closer tothe edge of the acetabulum A similar to a coxa valga deformity,resulting in similar degeneration of the articular surface along the rimof the acetabulum. Radiographically, an abnormal acetabulum isidentified by measuring the Center-Edge angle of Wiberg, AcetabularDepth ratio, Femoral head extrusion ratio, the Lequense anteriorcenter-edge angle etc.

In coxa vara (FIG. 32B), the line of action of the hip abductor musclesis steeper, leading to a more medial resultant force R, therebyincreasing the chance of hip dislocation.

Referring now to FIGS. 33A-B, an exemplary embodiment of the presentinvention as applicable to correction of hip dysplasia is schematicallyillustrated. In the illustrated exemplary embodiment, implant 220 isinstalled between the gluteus minimus GMin and the rectus femoris RF.However, implant 220 may be installed in any desired location betweenthe hip capsule and at least a portion of the hip abductor muscles so asto achieve a desired resulting force vector M. In some embodiments,implant 220 would be placed in the tissue between the gluteus musclesand the ligaments L. The implant 220 is installed in a desired location,and may be implanted arthroscopically or using a mini-open or openapproach, using surgery, a balloon catheter, or another suitableprocedure. As described in connection with other embodiments, implant220 generally includes a support portion that is configured to besecured by or to surrounding tissue and a bearing portion configured toatraumatically engage and displace target tissues. A variety ofalternatives for both the support and bearing portions are describedherein.

The implant 220 may be formed of various materials. In some exemplaryembodiments, implant 220 is constructed of a material with sufficientrigidity to displace the target tissue with a smooth outer surface tominimize friction, allowing the target tissue to slide along the implantwithout injury as the joint is moved. Metals such as stainless steel ortitanium, or biocompatible polymers may be used. Alternatively, implant220 may be partially or entirely constructed of a soft, compliantmaterial and may be, for example, a compliant outer membrane filled witha fluid such as water, saline, silicon, hydro gels, gasses, and soforth. Implant 220 may be inserted in an evacuated state and filled insitu after placement, or the prosthesis could be a sealed elementpre-filled with gel, fluid, polymeric or metallic beads, or other fluidor with flexible or flowable materials.

Implant 220 may also be a solid, e.g., polymeric or metallic, body ofsuitable atraumatic shape. A fixed shape implant 220 may alternativelyinclude a bag with an inlet through which a curable material such asbone cement may be injected and allowed to harden. The curable materialmay also be polymerizable hydrogels that are cured by exposure toradiation (e.g. UV light, visible light, heat, X-rays etc.). Thematerial may be cured by direct or transdermal exposure.

The surface of the implant 220 could be textured or smooth. A solid orcompliant implant 220 may include exterior padding or a lubricious outercovering or coating to facilitate the sliding movement of the musclesand tendons along or over the prosthesis. Such padding, coating, orcovering may cover a portion of, or all of the exterior of the implant220. The padding or coatings may, for example, align to support or aligna muscle or ligament. The implant may also have extensions that coverthe anterior and/or posterior regions of the hip capsule, therebyreinforcing the capsule.

The implant could have a shape or feature adapted to guide the musclesand tendons and retain their position on the implant. For example, agroove or trough could be provided on the outer surface of theprosthesis through which the muscles and tendons would extend. Thesemuscles and/or tendons are aligned with the groove when the implant isinstalled. Alternatively, the implant could include a ring or eyeletwith a discontinuity to allow placement of the ring or eyelet around themuscles/tendons.

FIGS. 34A and 34B show effects of the implant 220 on the hip abductorforce M in accordance with an embodiment. As can be seen in FIG. 34A,the hip abductor muscles HA, prior to installation of the implant 220,extend in a first direction. A force concentration M toward the lateraledge of acetabulum A may be seen. After installation of the implant 220,as shown in FIG. 34B, the hip abductor muscles HA are displacedoutwardly away from the joint, increasing the angle and the length ofthe moment arm h of the force exerted by the abductor muscles relativeto the central axis of the joint. As a result, the resultant force Rthrough the femoral head to counteract the body weight force moves morecentrally into the joint and away from the lateral edge of theacetabulum A. As such, the resulting force vector R may be more properlyaligned to press the femoral head FH into full contact with theacetabulum A, or to otherwise provide a more desirable force arrangementfor the hip.

As with other embodiments of the present invention, prostheses fortreatment of hip disorders according to the present invention mayinclude suitable anchors for affixing implants in place, and/or may bestabilized by the surrounding muscle and/or ligament structures. In anembodiment, the prosthesis extends from the pelvis P to the femur F, andmay be anchored at one or both of these sides, or may not be anchored atall. Shape, materials or surface texture may be incorporated into thesupport portion to facilitate and maintain placement by surroundingtissue. Tabs or other features may be provided for an implant to aid inanchoring or positioning the implant in a desired manner with respect tothe pelvis P and/or the femur F. Either the femur side or the pelvisside of an implant may include one or more such tabs to attach and/or toarrange the implant in a desired manner. The implant may be a standardshape, or may be custom made for a particular application, eitherthrough planning process as described below or inter-operatively.

As an example, FIG. 35 shows a prosthesis 224 that anchors to the femurF and the pelvis P. The prosthesis 224 includes a main body 223 forminga bearing member and a support member including fixation tabs. First tab225 has an opening 226 to anchor prosthesis 224 to the greatertrochanter and second tab 227, on the opposite end, has an opening 228to anchor to the pelvis. The body 223 may have various shapes includingrectangular prism, sphere, egg-shape, cylinder, conical, trapezoidal, orothers as appropriate to achieve the desired realignment of forces inthe joint. The prosthesis 224 may be used to shift the force vector Mfor the hip abductor muscles of a hip joint as described above.

A suture anchor, bone tack, bone screw or other suitable attachmentstructure may be utilized to attach the trochanter side of theprosthesis 224 utilizing the opening 226. In a similar manner, theopening 228 may be utilized to anchor the prosthesis in the pelvis. Theanchoring device may be placed percutaneously after the implant has beenpositioned.

As described above, embodiments of prostheses may be installed andfilled with a fluid in situ. To this end, an access port 229 may beprovided for filling the prosthesis 224 either during surgery or may beinstalled so that it is accessible after surgery.

As another example, as shown in FIG. 36, a prosthesis 230 includes abody having a wishbone shape, with a main stem 240 and two legs 232, 234for a femur side of the prosthesis forming at least part of a bearingmember. Each of the legs 232, 234 includes a tab 233, 235 extendingtherefrom, each with an anchor opening 236, 238. The fixation tabs format least a part of a support member. The main stem 240 is provided forthe pelvis side of the prosthesis, and includes an anchor opening 242.

The two tabs 233, 235 may, for example, be anchored on opposite sides ofthe greater trocanter G. As other alternatives, a femur side of aprosthesis may be fixed or otherwise anchored to the femoral neck F, orat a location on the femur F below the greater trochanter G. The mainstem 240 may be fixed to the ilium I, the ischium IS, or anothersuitable location on the pelvis P, either on the posterior or anterioraspect. As an alternative to the arrangement in FIG. 36, two tabs may beprovided on the pelvis side of the prosthesis 230. These two tabs may beanchored, for example, one on the posterior and one on the anterior sideof the pelvis.

FIG. 37 shows another embodiment of a prosthesis 244. Like theprosthesis 230, prosthesis 244 includes two legs 246, 248 on the femurside of the prosthesis, and a main stem 250 that aligns with a pelvisside of the hip joint when the prosthesis is installed. However, unlikethe prosthesis 230, the prosthesis 244 does not include structures, suchas tabs and/or anchoring holes, for anchoring of the prosthesis to thefemur. As described above, such a prosthesis 244 may be fixed in placeby the surrounding muscle structures, which are layered tightly aroundthe hip capsule. Similarly, the main stem 250 does not include a taband/or an anchor for attachment to the pelvis.

If desired, as an alternative, a prosthesis may be anchored only on afemur side or a pelvis side and/or may include legs on either side whichmay be anchored or held in place by muscle structure. As an example, asingle anchor, such as a tab and/or an opening, may be provided oneither or both of the legs 246 or 248, and/or an anchor may be providedon the main stem 250. Any combination of anchors or muscle stabilizedsupport may be used. In such embodiments the bearing and support membersmay be integrated.

In accordance with another exemplary embodiment, a prosthesis may havevarying thickness so as to provide varying displacement of the abductormuscles and/or hip tissues. As an example, as shown in FIG. 37, theprosthesis 244 includes three areas having different thicknesses, X, Yand Z. The thickness X corresponds with the leg 246, the thickness Ycorresponds with the leg 248, and the thickness Z corresponds with themain stem 250. Varied thickness may also be used along a leg or stem, oracross the leg or stem. These areas of varied thickness X, Y and Z maybe utilized to advantageously fit the prosthesis 244 in the hip joint H,and/or to provide a desired force offset. Prosthesis 244 may bepre-shaped to have the varied thickness prior to implantation, or eachportion of the prosthesis may be separately enlarged to the desiredthickness in situ by, e.g., filling with a desired volume of inflationmedium to achieve the desired thickness.

FIG. 38 shows an anterior view example of a prosthesis 260 installed ina hip joint H in accordance with an embodiment. FIG. 39 is arepresentation of the prosthesis 260 in place, with the ligaments L andthe abductor muscles removed to show detail. In the embodiment shown inFIG. 38, prosthesis 260 includes a pelvic tab 262 and a femur tab 264,forming at least part of a support member and both extending from acentral, rounded, bulbous main section 265 forming a bearing member. Thebulbous configuration of the main section 265 aids in a desireddisplacement of the abductor muscles. Pelvic tab 262 and femur tab 264may be a thin and highly flexible material to minimize any impact onjoint articulation. The pelvic tab 262 is anchored to the pelvis, forexample via a pin 266, bone screw, suture, or other suitable anchorfixed to the ilium 1. An opening may be provided in the tab for theanchoring function. The femur tab 264 is anchored by a suitable anchor,for example a pin 268, to the greater trochanter G, femoral neck, orother suitable location. The main section 265 in the embodiment shown inFIG. 38 is centrally mounted, and is arranged so that, when theprosthesis 260 is installed, the main section 265 is positioned betweenthe capsular ligaments L and muscle structure of the gluteus minimusGMin and gluteus medius GMed. However, the main section 265 may bepositioned closer to either the pelvis attachment or the femoralattachment, and may be arranged at other locations so as to desirablyalter the force vector M.

In accordance with additional embodiments, illustrated in FIGS. 40-42,an implant may be attached only to the femoral neck N, by a supportmember and/or may extend transverse to the femoral neck. In this manner,the prosthesis may provide a bearing member for displacement of a largeramount of muscle and/or tissue around the girth of the femoral neck Nand/or may be more easily maintained in place due to direct attachmentaround at least a portion of the femoral neck N. Such a prosthesis maybe dog bone or kidney shaped so as to nest around the capsule ligamentsL or femoral neck N on one side. Typically, a dog bone shape includes anarrowed, usually elongate, central section, and a bulbous, or rounded,larger diameter shaped at each end. A kidney shape, on the other hand,is more bean shaped, with two outer ends extending in one direction sothat a groove or indentation is formed on a side of the shape. Foreither shape, a groove or other shape may be provided on the other sidethrough which the tendons and muscles may slide without slipping off theprosthesis. Deformable pillow-like structures filled with gel, foam, orbeads may also be used to conform to or partially wrap around thecapsule ligaments L or femoral neck N.

As an example, as shown in FIG. 40, dog bone shaped prosthesis 270extends transverse to and nests around a femoral neck N and/or theligaments L. The dog bone shaped prosthesis 270 in FIG. 40 includes anarrow central section 271 between two outer, bulbous, rounded ends 273.The narrow section is of sufficient length so that the two ends nest onopposite sides of the ligaments L or femoral neck N. In the embodimentshown in FIG. 40, the prosthesis is attached by two anchors, such aspins or screws 272, 274, through the central section 271 into thefemoral neck N. However, as described in previous embodiments, aprosthesis may be installed without fasteners, or the prosthesis may beanchored in another way or location. An upper part of the prosthesis 270may channel muscles through the upper saddle formed between the two ends273 and along the central section 271 of the dog bone shaped prosthesis270.

FIG. 41 shows another embodiment of a prosthesis 280 that extendstransverse to a femoral neck. The prosthesis 280 is kidney-shaped, andincludes a narrower central section 283 and two outer, rounded ends 284.An indentation 285 is formed between the ends. In an embodiment, theprosthesis is shaped so that the indentation matches the curvature ofthe femoral neck and/or ligaments L onto which the prosthesis attaches,and thus the prosthesis nests at least partly around the femoral neck Nwhen installed. In the embodiment shown in the drawings, an optional pinor screw 282 is used for anchoring the prosthesis 280 to the femoralneck N, but other anchors, or no anchor at all, may be used.

As another alternative, a prosthesis may be anchored to the femoral neckutilizing a U-shaped or C-shaped bracket or band or other structure thatextends around the femoral neck. As an example, FIG. 42 shows aprosthesis 290 mounted on a U-shaped bracket 292 that extends around afemoral neck N and/or ligaments L. The U-shaped bracket 292 is curved tofit closely around the femoral neck N and includes a bolt 293 thatextends through openings (not shown) on ends of the bracket and along anopposite side of the femoral neck. The bolt 293 may be used to lock theU-shaped bracket 292 in place. The prosthesis 290 in FIG. 42 isbulbous-shaped, but the U-shaped bracket 292 may alternatively be usedwith other shapes of prostheses, such as the dog bone shaped prosthesis270, or the kidney-shaped prosthesis 280.

In accordance with further embodiments, a prosthesis may be mounted as acap on the greater trochanter G for displacing hip abductor muscles. Asan example, FIG. 43 shows a prosthesis 296 mounted as a cap on thegreater trochanter G. The prosthesis 296 includes a horizontal extension298 and a vertical extension 2100 that form an L-shape that extendsupside down against the greater trochanter G. In the embodiment shown inFIG. 43, the prosthesis 296 is anchored by pins 2102, 2104, but may beanchored or attached in another manner, including a U-shaped or C-shapedbracket or band or other structure that extends around the femoral neck,as described above. As can be seen in FIG. 43, the prosthesis 296 isrounded on an outer side, and projects laterally from the hip so as tosubstantially displace the hip abductor muscles HA. In this exemplaryembodiment, the bearing and support members are combined in a mannersimilar to implant 40 as described above.

To aid the hip abductor muscles HA and/or tendons or other tissuesliding over the prosthesis 296 or another cap prosthesis, the outersurface of the cap may be lubricious. Alternatively, a guide or otherstructure may be provided for maintaining tendons and muscles in place,and for providing a sliding feature. As an example, as shown in FIG. 44,a prosthesis 2110, which may be shaped like the prosthesis 296, includesa groove or channel 2112 for slidably receiving and guiding the hipabductor muscles HA as prosthesis 2110 moves with the femur. Otherstructures, such as rings, eyelets, tunnels, or other features may beused to guide and position the hip abductor muscles HA and/or ligamentsand tendons.

As another example, a prosthesis, such as the prosthesis 2120 shown inFIG. 45 may include one or more external rollers 2122 for permitting thehip abductor muscles HA to roll over the prosthesis 2120 as the femur Fmoves. The prosthesis 2120 includes a series of three rollers 2122rotationally mounted to the lateral and/or superior surface ofprosthesis 2120 so as to align with the hip abductor muscles HA andtheir primary direction of movement.

In accordance with another embodiment, a prosthesis may be configured toexpand in situ so that the prosthesis may be inserted into a body in acontracted state via a cannula or mini-open procedure, expanded in situ,and installed in the expanded state. As an example, a device may includeone or more hinges or may be flexible so that it may contract to a smallspace, and expand when installed. A spring or other device may be usedfor expanding the prosthesis, or the device may be expanded mechanicallyor in another manner. An example is shown in FIGS. 46-49, where aprosthesis 2130 includes two legs 2132, 2134 connected by a hinge 2136.The two legs 2132, 2134 form a cap that may be fitted as a supportmember, for example, on the greater trochanter G or on the femoral neckN.

Delivery device 2138 may be provided that captures the hinge 2136 andkeeps the legs 2132, 2134 together during insertion, and opens the legsduring installation. The delivery device 2138 includes a tubular shaft2135 configured for receiving the hinge 2136 and legs 2132, 2134 withinthe shaft during delivery. The walls of the delivery device 2138 capturethe legs 2132, 2134 and keep the legs closed during insertion.Prosthesis 2130 is held in the shaft by means of friction with the innerwall thereof, or, optionally, an inner shaft (not shown) may be slidablypositioned in shaft 2135 which has a distal coupling mechanism adaptedto releasably grasp hinge 2136.

Once the prosthesis 2130 is inserted by the delivery device 2138,retraction of the delivery device may cause the prosthesis to expand, orthe prosthesis may be expanded mechanically or in another manner. As anexample, an inner shaft (not shown) may be releasably coupled to theprosthesis 2130, the actuation of which causes the legs 2132, 2134 toopen and the prosthesis to release from the delivery device. The legs2132, 2134 may be separated during installation to fit around, forexample, the femoral neck N (FIG. 47) and/or the ligaments L, or thegreater trochanter G. In an installation embodiment, for example, theprosthesis 2130 may be expanded around the femoral neck N (FIG. 48) andmay be moved over and then installed on the greater trochanter G.

Use of the prosthesis 2130 provides minimally invasive surgery, due tothe ability to install the prosthesis while closed. Thus, a smallincision may be used, and/or the prosthesis may be installed through acannula. The device, once installed, may be anchored in place via pinsor other suitable fasteners, or may be held in place by the muscle ortissue structure around the femur F.

Prosthesis 2130 may be configured to expand outward to form a cap to fitover the greater trochanter G as shown in FIG. 48 or to fit in asuitable manner around a portion of the femoral neck N as shown in FIG.49. As another embodiment, a prosthesis may include two or moreelements, such as hinged or folding elements, that connect together toform a contiguous implant. As an example, two or more hinged or foldedelements could be introduced into a space and then locked together toform a contiguous implant. Locking multiple elements together can beachieved through alignment of features, the elements may be snap lockedtogether, or the elements may be connected by fasteners, crimping, oranother suitable manner. As an alternative, multiple elements might nesttogether when put into place and may be attached adjacent to one anothervia suitable fasteners such as bone screws, tacks, pins or otherfasteners. In an embodiment, each element or part is expanded in situ.

An example of such prosthesis 2140 is shown in FIG. 50, where a firsthinged element 2142 is butterfly-shaped, with first and secondcrescent-shaped, wishbone-shaped, or triangular legs 2144, 2146connected by a hinge 2148. The two crescent-shaped legs 2144, 2146 arearranged so that the concave portion of each of the legs faces outwardand directly opposite each other. A second hinged element 2150 alsoincludes two similar crescent-shaped legs 2152, 2154 attached by a hinge2156. The two hinged elements 2142, 2150 may be attached to each otherprior to implantation, or may be introduced separately and attached insitu. The two hinged elements 2142, 2150 may be installed by, forexample, first installing the first hinged element 2142, and theninstalling hinged element 2150 on top of and nested around the firsthinged element 2142. In each case, the hinged elements are folded beforeand during installation, and expanded in situ. The hinged elements 2142,2150 may be anchored in a suitable manner, for example at anchorlocations 2160 to a position throughout the prosthesis 2140. One suchanchor position may be at the overlap of the two hinges 2148, 2156. Asshown in FIG. 51, the prosthesis 2140 may be mounted, for example, onthe greater trochanter G or in another suitable location.

In accordance with another embodiment, a belt, strap, or other tensionmechanism may be extended around and tightened on the femoral neck N andthe hip abductor muscles HA and/or the hip capsule ligaments/tendons.The band or strap or other structure may be tightened to increasetension, thereby increasing the force pulling on the femur F. Thisapproach might be used, for example, where the increased tensionproduces a resultant force suited for the particular pathology of thepatient. For example, for patients with excessive loading on the medialside of the joint, the belt may be used to increase tension on thelateral side of the joint producing a higher lateral force component andreducing loads on the medial side of the joint. In such an embodiment,the belt or strap would extend around the femoral neck and the hipabductor muscles and/or capsule ligaments/tendons on the lateral side ofthe joint, but would extend under the hip abductor muscles/tendons onthe medial side of the joint. For patients with excessive loading on thelateral side of the joint, the arrangement of the belt or strap may bereversed.

As with previous embodiments, the belt or strap could have a lubriciousinterior surface to allow sliding movement of the muscles relative tothe belt or strap. The belt or strap may optionally extend only part ofthe way around the femoral neck and may be a rigid partial ring or hoop.The belt or strap may optionally be fixed to the femoral neck by one ormore anchors, such as a pin or screw. The belt or strap may be flexible,or it may be a rigid ring or hoop, composed of fabric, metal or apolymer. A rigid structure may be circular, oval, racetrack, or anothersuitable shape, and may have a discontinuity to allow insertion aroundthe muscles and the femoral neck N. The belt or strap may be elastic toact like a spring, or may be non-distensible.

An example of such a belt or strap is shown in FIG. 52, where a strap2170 extends around the femoral neck N and the hip abductor muscles HA.The belt or strap may take many forms, and may be arranged as needed fora desired force effect. In such embodiments the bearing member is formedto act inwardly and the support member is opposite and surrounds thebone or other tissue at the fixation location.

If desired, the belt or strap, such as the belt or strap 2170, mayinclude an adjustment mechanism to allow cinching of the belt or strapto increase tension in the muscles and/or ligaments. Examples ofcinching mechanisms that may be used are shown in FIGS. 53-56. In FIG.53, a one-way clamp is provided that allows a physician to install thetension strap and pull on a free end 2182 to cinch the strap 2180 aroundthe femoral neck N and the hip abductor muscles HA. The device in FIG.53 includes a catch strap 2183 and a pawl 2184. The strap 2180 includesa number of openings 2186 along its length. An installer pulls on thefree end 2182 of the strap, pulling up to keep the openings fromcatching on the pawl 2184. The catch strap 2183 maintains alignment ofthe free end 2182 when pulled. When the strap 2180 is tight, theinstaller pulls down on the free end 2182 and aligns the pawl 2184 witha desired opening 2186 on the strap. The catch strap 2183 and the pawl2184 hold the free end 2182 in position.

Another example of one-way clamp 2190 is shown in FIG. 54, in which pawl2192 engages teeth 2194 on a strap 2196. The teeth 2194 include a slopedfront side and a blunt rear side. The pawl 2192 engages the blunt rearside to prevent retraction of the teeth 2194. The sloped front sidespermit indexing of the teeth in one direction past the pawl 2192 when aphysician pulls on the free end of the strap 2196.

Another example of a cinching mechanism is shown in FIG. 55, where adevice 2200 is configured like a hose clamp and includes a screw 2202that engages openings 2204 in a strap 2206. Rotation of the screw 2202causes the strap to tighten or loosen depending on the rotationdirection.

FIG. 56 shows an example of another device 2210 that may be used as acinching mechanism. The device 2210 includes two rigid C-shaped members2212, 2214 connected at one edge by a hinge 2216 and at another edge byscrew 2218. The device 2210 may be tightened or loosened by rotation ofthe screw 2218.

FIG. 57 shows a prosthesis 2300, similar to the prosthesis 220, in whichthe prosthesis is connected to hip abductor muscles HA via a band 2302.The band 2302 anchors the prosthesis 2300 in place. The band 2302 may betied or clasped into place. In an embodiment, the band uses a cinchingmechanism, such as any of the cinching mechanisms described above, tocinch the band 2302 into place around the hip abductor muscles HA.Alternatively, a prosthesis, such as the prosthesis 2300, may beinstalled in position, and a band or belt may extend around the musclesor capsular ligaments to maintain the position of the prosthesis withoutthe belt being attached to the prosthesis. In this manner, the band orbelt aids in capturing the prosthesis in place.

In another embodiment of the present invention, illustrated for examplein FIGS. 58-60, an implant 3100 for treatment of hip disorders is shapedto jog around the insertion point(s) of connective tissues (includingtarget tissues) around the joint. Depending on specific joint anatomyand patient conditions, the implant may be designed to permit securefixation at a suitable site while still placing the bearing anddisplacement portion under the target tissue while minimizing trauma toimportant intervening tissues. For example, as shown in FIGS. 58 and 60,implant 3100 may include three sections—anterior section 3110, superiorsection 3120 and posterior section 3130. Sections 3110 and 3130 aresupport members providing the fixation sections and may include meanssuch as screw holes 3114, 3134 to accommodate bone screws 3112 (as shownin FIG. 58) for securing to the bone. Section 3120 comprises bearingmember 3122 with a bearing surface 3124 as described herein above.

Implant 3100 may be of unitary construction or may include two or moreinterlocking units assembled together. The different sections could bemade for identical materials or different materials, for example thebearing section 3120 may be fabricated out of pyrolytic carbon and thefixation sections from titanium or other similar bone compatiblematerial.

In order to address the specific anatomy, anterior section 3110 may beshaped to attach to the femur by circumventing muscle attachment sitessuch as for the Gluteus minimus (GM), Piriformis (P), and Obturatorinternus and superior and inferior gemelus (O). Other sites to beavoided include the vastus lateralis medially, and the vastusintermedius and medialis superiorly. Posterior section 3130 may beshaped to attach to the femur between the attachment sites of thequadratus femoris and the iliopsoas muscles. In the sagittal plane,sections 3110 and 3130 also may be shaped as needed to avoid any muscles(non-target tissue) that are traversing medial to lateral.

In a further alternative embodiment, instead of installing a device, afluid may be injected into the desired space within or adjacent to thehip abductor muscles that hardens to a solid, allowing the fluid toharden into a solid, the solid then providing the function of theprosthesis. As examples, the prosthesis may be injected as a liquifiedpolymer or foam material into the space between the gluteus muscles andfemoral neck and allowed to harden. The material could have adhesiveproperties to stick to the capsular ligaments around the femoral neck. Aballoon or other expandable member or retractor could be inserted tocreate space between the femoral neck and the gluteus muscles into whichthe material is injected.

In another aspect of the present invention, the principals and teachingsmay be applied in the veterinary context to the articular joints ofanimals. One exemplary embodiment of such a veterinary application isthe canine hip. The general arrangement of the bones associated with acanine hip, with reference to the hind limb, is illustrated in FIGS. 61Aand 61B. As indicated in FIG. 62, force plate studies have shown thatthe peak vertical force that the rear leg exerts on the floor during thestance phase of a gait cycle varies between 24% and 41% of the totalbody weight. Dogs place more load on their front legs, between 53% and65% of their body weight. During the midstance phase of the gait cycle,the orientation of the femur with reference to the pelvis is shown inFIG. 63.

Of particular interest in canine hip dysplasia are the forces acting onthe frontal plane (abduction/adduction) during the three legged stance(i.e. with one pelvic limb raised) of the gait cycle. A two dimensionalbiomechanical model of the canine hip is shown in FIG. 64, in which Irepresents the ilium; S, the sacrum; H, the femoral head; F₀, the forcedue to gravity; M₀, the moment induced by the axial musculature; F_(a),abductor muscle force; F_(h), hip reaction force; θ_(a), angle ofapplication of F_(a); θ_(h), angle of application of F_(h).

In a three-legged stance model, the external forces acting on the canineframe must be balanced by the internal forces to achieve equilibrium.External forces include the force F₀ exerted by the gravity forces ofthe trunk and head, and moment (torque) M₀ exerted by the twistingforces of the axial musculature. The canine hip joint is subjected toloads greater than the body weight due to additional abductor muscleforces and the pelvic torque. The hip force F_(h) and the abductor forceF_(a) are directly affected by the femoral neck angle and theabduction/adduction angle of the weight bearing pelvic limb. A largefemoral neck angle decreases the distance between the femoral head andthe greater trochanter, thus requiring greater abductor muscle forces toovercome the shortened lever arm. This increased muscle force results inan increased hip force. Additionally, the greater the abductor muscleangle θ_(a), the greater the hip force angle θ_(h). The increased θ_(h)results in increased loading of the rim of the acetabulum which resultsin the degeneration of the acetabular cartilage leading to hiposteoarthritis. A decrease in the femoral neck angle will increase thelever arm distance and thereby decrease both the abductor muscle forceF_(a) and the resultant hip force F_(h).

Excessive loading of the rim of the acetabulum may also occur when theacetabular coverage of the femoral head is insufficient and theresultant hip force F_(h) acts closer to the rim of the acetabulum. Thisoccurs when the acetabulum is insufficiently ventroverted.

Surgical interventions to address hip dysplasia involveintertrochanteric osteotomy (ITO) whereby the femoral neck angle isdecreased to reduce the hip force or triple pelvic osteotomy (TPO)whereby the acetabular ventroversion is increased. One study analyzingthe hip forces after TPO concluded that increasing the ventroversionfrom 0 degrees to 20 degrees provided the most benefit, while increasingventroversion from 30 degrees to 40 degrees provided limited benefit.The study also concluded that the beneficial clinical results of TPO maybe a result of the reduction in the magnitude of forces acting on thehip joint acting in concert with the increased coverage of the femoralhead.

In one exemplary embodiment of the invention, implant 4100 is placed onthe femur under the hip abductor muscle complex (e.g. gluteus medius,gluteus profundus etc.) as shown in FIG. 65. In this manner, the forcevectors can be altered similar to the biomechanical changes associatedwith an osteotomy but without the need for such invasive surgery. Animplant such as implant 4100 would be appropriate for dogs with largefemoral neck angles as well as insufficient acetabular ventroversion.

While implant 4100 may be placed around the area of the greatertrochanter, it will be appreciated by persons of ordinary skill in theart that the implant may also be placed in other regions (e.g. femoralneck) so as to achieve the appropriate displacement of the abductormuscles. As shown in FIG. 66, the displacement of the abductor musclesalters the line of action of the abductor muscles. This displacementincreases the lever arm of the abductor muscles thereby reducing theabductor muscle force necessary to achieve mechanical equilibrium duringthe gait cycle, thereby reducing the resultant hip force. Additionally,the change in the abductor muscle angle θ_(a) results in altering theresultant hip force angle θ_(h), directing in more medially. This changein the direction of the resultant hip force would reduce the load on therim of the acetabulum as well as potentially improve the stability ofthe joint.

As with other embodiments described herein, implant 4100 would bedesigned to not interfere with any of the muscle insertion points in thearea of the greater trochanter. As also elsewhere described inconjunction with exemplary embodiments of the present invention, implant4100 may be attached to the underlying bone using anchors, screws, wiresor other means of fixation. The prosthesis may include multiplecomponents, for example, the prosthesis may include an anteriorcomponent which is attached to the anterior region of the femur, aposterior component which is attached to the posterior region of thefemur, and a third component which is attached to the other twocomponents and effect the displacement of the abductor muscles.

Implant 4100 also could be implanted arthroscopically or using amini-open or open approach. The thickness of the implant may be adjustedduring surgery or anytime after surgery. This could be accomplished bymechanical means. The bearing surface of the implant could be texturedor smooth. The surface in contact with bone may be textured or porous toenhance bone in-growth while the surface in contact with the soft tissuemay be smooth to enable easy tissue motion.

An exemplary treatment regiment in accordance with an embodiment of theinvention is illustrated in FIG. 67. For purposes of illustration, thisexample is described in the context of a hip treatment, but as will beappreciated by persons of ordinary skill in the art, the process isequally applicable to other locations as taught herein. Beginning at1000, a plan is made for installation of a prosthesis, such as theprosthesis 220. At 1002, the prosthesis is installed, for example bysurgery as described above.

The planning 1000 may involve any number of different regimens. Part ofa plan 1000 may involve a particular physician evaluating a hip joint inaccordance with well-known procedures, and selecting and installing aparticular prosthetic based upon an evaluation. A prosthesis may beselected, for example, from among the many embodiments described herein,or a combination of prostheses may be selected.

As another example of a plan 1000, a computer model of a hip joint H maybe generated, permitting a physician to determine, via a visual model ofthe hip joint, where a prosthesis should be installed and/or todetermine what type of prosthesis should be installed. In an embodiment,preoperative images (X-ray, MRI etc.) are used to determine thedimensions of the implant and the optimum location of the implant.Information such the Center-Edge angle of Wiberg, Acetabular Depthratio, Femoral head extrusion ratio, the Lequense anterior center-edgeangle, CCD angle etc. may be used in the analysis. The implant may beselected from a set of standard sizes or an implant that is shapedintra-operatively or a custom implant that has been fabricated to meetthe specific patient need.

As another example of planning 1000, a given prosthesis may be thedefault prosthesis for particular abnormal structures or symptoms of ahip, or may be preferred for particular abnormalities. For example, inan embodiment, implant 220 as described above may be appropriate forpatients with a shallow acetabulum A, or with coxa valga. Otherprostheses described herein may be more appropriate for other hipabnormalities. Similar planning may be used to treat pathologies of theknee, shoulder, ankle and elbow.

Further alternative exemplary embodiments of the present invention aredescribed in the paragraphs below.

In one example, an apparatus for treating an articular joint, whereinthe joint includes at least first and second bones with facing articularsurfaces and the bones are subject to forces exerted by target tissuesaround the joint, comprises a support portion adapted for being securedto tissue or bone, and a bearing portion supported by the supportportion. The bearing portion is configured and dimensioned for placementproximate the target tissue. The bearing portion has at least onebearing surface configured to displace the target tissue relative to thejoint by a distance sufficient to redirect a force exerted by the targettissue on the joint to achieve a therapeutic effect. Such an exemplaryapparatus may also include one or more of the following features:

At least one bearing surface adapted to atraumatically engage targettissue.

The support portion underlies the bearing portion and comprises asupport surface opposite the bearing surface adapted to contactunderlying tissue.

Attachment means for securing the bearing portion to the underlyingtissue.

Constructed of or including a soft compliant material.

Constructed of or including a rigid material.

The support surface adapted to contact at least one of the first andsecond bones.

Attachment means for securing the support portion to the bone.

Means for securing the implant to soft tissue, which may be configuredto secure the implant to the target tissue.

The support portion comprises a support member and the bearing portioncomprises a bearing member.

The bearing member is a separate member from the support member.

The support member and bearing member form a single integral structure.

The bearing member is adjustable with respect to the support member tocontrol the displacement of the bearing surface from the supportsurface.

An adjustment mechanism cooperating between the bearing member and thesupport member.

The adjustment mechanism comprises a screw adjustment.

The adjustment mechanism is configured to be adjusted after the supportsurface is secured to the tissue or bone.

The adjustment mechanism comprises a wedge adjustment.

The bearing member is a material different from the support member.

The bearing member is a soft compliant material.

The bearing member is made from a material comprising silicone,titanium, stainless steel or pyrolytic carbon.

The bearing member is configured to provide varying amounts ofdisplacement of the target tissue in response to joint flexion angle.

The bearing member has a ramp shape.

The ramp shape is configured and dimensioned to allow the target tissueto move along the ramp to varying degrees of displacement as the jointis moved through different angles of flexion.

The bearing member defines depressions for receiving and guiding thetarget tissue.

The implant is configured to displace the target tissue in a firstdirection generally orthogonal to the bearing surface and in a seconddirection generally parallel to the bearing surface.

The bearing surface is a low friction material.

The support member has a fixation portion and a displacement portion,with the bearing member being disposed in the displacement portion.

The fixation portion includes means for facilitating fixation to thebone.

The displacement portion is configured and dimensioned to be receivedaround a portion of the greater trochanter or femoral neck, and thefixation portion includes a first part configured and dimensioned toextend anteriorly from the bearing portion between the attachments forthe piriformis and gluteus minimus, and to extend posteriorly betweenthe attachments for the quadrates femoris and the iliopsoas.

The fixation portion is configured and dimensioned to be received arounda portion of the femoral neck, and the displacement portion isconfigured to extend around at least a portion of a hip abductor muscleto displace the muscle towards the femoral neck.

The support member further comprises a spanning section between thefixation portion and the displacement portion.

The spanning section is configured and dimensioned to avoid selectanatomical features located between a fixation location and targettissue displacement location.

The fixation portion is configured and dimensioned to be secured againstthe femur cranially with respect to the lateral head of thegastrocnemius, the spanning portion is configured and dimensioned toextend posteriorly around the lateral head of the gastrocnemius, and thebearing portion is configured and dimensioned to extend caudally withrespect to the lateral condyle and underlie at least one of the fibularcollateral ligament and the biceps femoris tendon.

The fixation portion is configured and dimensioned to be secured againstthe tibia adjacent to Gerdy's tubercle and the soft tissue to bedisplaced is the iliotibial band, the displacement portion is configuredand dimensioned to extend cranially from the tibia to a positionproximate the iliotibial band, and the spanning section is configuredand dimensioned to extend laterally from the fixation portion to thedisplacement portion.

The fixation portion is configured and dimensioned to be secured againstthe tibial tuberacity, the spanning section is configured anddimensioned to extend cranially from the fixation portion, and thedisplacement portion is configured and dimensioned to extend mediallyfrom the spanning section and over a central portion of the tibialcondyles proximate the patellar tendon.

In another exemplary embodiment of the present invention, an apparatusfor treating an articular joint to effect force distribution in thejoint, the joint including at least first and second bones with facingarticular surfaces, the bones being positioned with respect to oneanother by associated muscle and connective tissues, the tissuescomprising target tissues for therapy, comprises a bearing memberconfigured and dimensioned for placement in a therapeutic locationunderlying at least one target tissue, the bearing member having athickness sufficient to displace the target tissue from its natural pathto a therapeutic path when placed in the therapeutic location, and abearing surface disposed on the bearing member, the bearing surfacebeing configured to atruamatically engage the target tissue and topermit movement of the target tissue there along. Such an exemplaryapparatus may also include one or more of the following features:

Dimensions of the bearing member are sufficient to displace targettissues by an amount and in a direction that reduces load on at least aportion of the articular surfaces.

Attachment means for securing the bearing member at the therapeuticlocation by attachment to surrounding tissue.

A support member supporting the bearing member.

The bearing member is a separate member from the support member.

The bearing member is adjustable with respect to the support member toselectively control displacement of the target tissue.

An adjustment mechanism cooperating between the bearing member and thesupport member.

The bearing member is a soft compliant material.

The bearing member is configured to provide varying amounts ofdisplacement of the target tissue in response to joint flexion angle.

The bearing member has a ramp shape.

The support member has a fixation portion and a displacement portion,with the bearing member being disposed in the displacement portion.

The support member further comprises a spanning section between thefixation portion and the displacement portion.

The spanning section is configured and dimensioned to avoid selectanatomical features located between a fixation location and targettissue displacement location.

A support surface disposed on the support member opposite the bearingmember, the support surface being configured and dimensioned to supportthe bearing member against tissue underlying the target tissue.

The support surface is adapted to contact another target tissue.

The support surface is adapted to contact at least one of the first andsecond bones for support thereon.

In a further exemplary embodiment of the present invention, an apparatusfor treating disorders of articular joints, the joint being subject toforces exerted by soft tissues disposed proximate to the joint,comprises a prosthesis implantable in engagement with the soft tissuesso as to displace the soft tissues sufficiently to alter the location,angle or magnitude of the forces exerted by the soft tissues so as toachieve a therapeutic effect in the joint. Such an exemplary apparatusmay also include one or more of the following features:

The articular joint is a hip joint and the prosthesis is configured anddimensioned to counter forces acting to create a dysplastic joint,wherein the wherein the hip joint is a human hip joint or a canine hipjoint.

The articular joint is a knee joint and the prosthesis is configured anddimensioned to counter forces acting to create an osteoarthritic jointand/or to counter forces acting to create excessive patellar compressionforce.

The prosthesis comprises anchoring means for anchoring the prosthesis ina fixed position relative to at least a portion of the joint.

The prosthesis displaces the soft tissues in a first direction away fromthe base tissue and in a second direction laterally relative to the basetissue.

The joint is surrounded by a capsule, and wherein the anchoring means isconfigured for fastening to soft tissue or bone outside of the capsule.

The prosthesis is a hard material.

The prosthesis comprises a soft outer layer defining a chamber andwherein the chamber is filled with a fluid or gel.

The prosthesis comprises a connector for filling the chamber with thefluid or gel after the prosthesis is implanted.

The prosthesis is bifurcated so as to have a wishbone, Y or V shape.

The prosthesis is configured to be mounted over the greater trochanteror femoral neck.

The prosthesis is configured to be mounted over the femoral lateralcondyle.

The prosthesis is configured to be mounted to at least one of the femur,pelvis, fibula, tibia, radius, ulna scapula, calcaneus, humerus, spinalvertebrae, tarsal, metatarsal, carpal, metatarsal, or talus.

The prosthesis is configured to be mounted to the tibia adjacent toGerdy's tubercle and the soft tissue to be displaced is the iliotibialband.

The prosthesis is configured to be mounted to the tibial tuberacity andthe soft tissue to be displaced is the patellar tendon.

In yet another exemplary embodiment of the present invention, a methodof treating an articular joint to effect force distribution in thejoint, the joint including at least first and second bones with facingarticular surfaces, the bones being positioned with respect to oneanother by associated muscle and connective tissues, comprises selectingat least one of the associated muscle and connective tissues as targettissue for treatment, displacing the target tissue without severing thebones or target tissue, and redistributing loading in the joint toachieve a therapeutic affect by the displacing. Such an exemplary methodmay also include one or more of the following features or steps:

The displacing is in a direction away from the joint.

The displacing comprises placing an implant under the target tissue.

The implant comprises a biocompatible member having a thicknesscorresponding to a selected tissue displacement.

The placing comprises inserting the implant under the target tissue at atherapeutically effective location, and securing the implant at thetherapeutically effective location without substantial restriction ofmovement of the target tissue.

The joint is a knee and the target tissue is located and displacedlaterally with respect to the knee.

The securing comprises attaching the implant to the target tissue.

The securing comprises attaching the implant to a soft tissue underlyingthe target tissue.

The securing comprises attaching the prosthesis to a bone underlying thetarget tissue.

The securing comprises attaching the prosthesis to a supporting tissueby suture, screw, staple, adhesive, or band.

The supporting tissue is at least one of the target tissue, a softtissue underlying the target tissue, bone underlying the target tissue.

The natural force exerted by the target tissue acts on the joint throughan effective moment arm, and displacing the target tissue moves thetarget tissue to a position wherein the effective moment arm isincreased.

The effective moment arm is increased by about 10 mm to about 30 mm.

The increase in effective moment arm is sufficient to increase torque byabout 20% to about 30%.

The target tissue is an iliotibial tract.

The target tissue is a lateral quadriceps-patellar tendon.

The target tissue is a biceps femoris muscle.

The target tissue is a biceps femoris tendon.

The target tissue is a popliteus muscle.

The target tissue is a lateral gastrocnemius muscle.

The target tissue is one or more abductor muscles.

The joint is the hip and the target tissue is at least one abductormuscle, which may include one or more of the gluteus minimus, gluteusmedius and/or gluteus maximus.

The joint is the knee and the target tissue is displaced anteriorly, thetarget tissue being one or both of the patellar tendon and or theiliotibial band.

Altering the target tissue displacement in response to joint flexionangle.

In a further exemplary embodiment of the present invention, a method oftreating an articular joint, the joint including at least first andsecond bones with facing articular surfaces, the bones being subject toa force exerted by target tissues around the joint, comprises implantinga prosthesis to displace the target tissue relative to the joint,wherein a force exerted by the target tissue is redirected in a mannerto redistribute a load on at least one of the articular surfaces withoutcutting the first or second bones. Such an exemplary method may alsoinclude one or more of the following features or steps:

The target tissue is displaced laterally, anteriorly or posteriorlyrelative to the joint.

The prosthesis is implanted on the same side of the joint as the targettissue.

Adjusting the magnitude of displacement of the target tissue after theprosthesis is implanted.

The joint is a knee, and the prosthesis is implanted on a first side ofthe knee to reduce loading on the articular surface of a second side ofthe knee. The first side may be the lateral side and the second side maybe the medial side.

The joint is a knee, and the prosthesis is implanted on the tibia toreduce loading on the femur.

The joint is the hip, and the prosthesis is implanted on a first side ofthe hip to move a resultant force in the joint away from the first side.The first side may be the lateral side The hp may be a human or caninehip.

The force exerted by the target tissue acts through a moment arm priorto displacing the target tissue and the target tissue is displaced tosubstantially increase the moment arm.

The force exerted by the target tissue opens the joint on a sideopposite the target tissue.

In yet another exemplary embodiment of the present invention, a methodof treating an articular joint, the joint including at least first andsecond bones with facing articular surfaces, the bones being subject toforces exerted by target tissues around the joint, comprises creating asurgical opening to access the target tissue, displacing the targettissue relative to the joint into a displaced configuration to redirecta force exerted on the joint by the target tissue without cutting thefirst or second bone; and closing the surgical opening with the targettissue remaining in the displaced configuration. The displacing maycomprise positioning a prosthesis under the target tissue.

In a further exemplary embodiment of the present invention, a method fortreating a hip joint having hip abductor muscles acting hereon,comprises installing a prosthesis in engagement with at least a portionof the hip abductor muscles or connective tissue connected thereto toalter a force vector applied by the hip abductor muscles to the hipjoint. Such an exemplary method may also include one or more of thefollowing features or steps:

The prosthesis is installed without cutting bone associated with the hipjoint.

The hip joint has a hip capsule and the prosthesis is installedsuperficial to the hip capsule.

The prosthesis displaces the hip abductor muscles to alter the forcevector.

The displacement of the hip abductor muscles is lateral.

The displacement of the hip abductor muscles is anterior or posterior.

The prosthesis alters the angle of the force vector relative to the hipjoint.

Installing comprises installing the prosthesis between gluteus musclesand capsular ligaments that surround the hip joint.

Installing comprises inserting the prosthesis in an evacuated state andfilling the prosthesis with a fluid.

Installing comprises inserting a bag having an inlet, and filling thebag with a curable material and allowing the curable material to harden.

The prosthesis includes a feature for guiding at least one of musclesand tendons, and wherein installing comprises aligning the one ofmuscles and tendons with the feature.

Anchoring the prosthesis to a pelvis and/or femur of the patient.

Anchoring the prosthesis to a femoral neck of the patient.

Installing comprises installing the prosthesis transverse to the femoralneck.

Installing comprises nesting the prosthesis around the femoral neck ofthe patient.

Installing comprises inserting the prosthesis in a contracted state andexpanding the prosthesis in situ into an expanded state.

Installing comprises inserting the prosthesis in a contracted state,installing the prosthesis in the contracted state and expanding theprosthesis in situ into and expanded state.

Installing comprises assembling two or more parts to form theprosthesis, each part expanded in situ.

Installing comprises injecting a fluid into the hip joint and allowingthe fluid to harden into the prosthesis.

Installing comprises attaching the prosthesis to soft tissue proximatethe hip joint.

The prosthesis is attached to at least a portion of the hip abductormuscles or connective tissue attached thereto.

Installing comprises extending a belt or strap around at least a portionof the hip abductor muscles and tightening the belt or strap around theat least a portion of the hip abductor muscles to alter the force vectorapplied by the hip abductor muscles.

The belt or strap draws the at least a portion of the hip abductormuscles toward the femoral neck.

Treating a hip joint comprises treating a hip joint of a human or anon-human animal.

Computer aided planning to prepare prosthesis shape and location.

Preparing the prosthesis shape inter-operatively.

In yet a further exemplary embodiment of the present invention, a methodfor treating a hip joint having hip abductor muscles acting thereon,comprises installing a prosthesis in engagement with a greatertrochanter of the hip joint to alter a force vector applied by the hipabductor muscles to the hip joint. Such an exemplary method may alsoinclude one or more of the following features or steps:

The prosthesis is mounted on the greater trochanter of the patient toform a cap over the greater trochanter.

Installing comprises inserting the prosthesis in a contracted state andexpanding the prosthesis in situ into an expanded state.

Installing comprises assembling two or more parts to form theprosthesis, wherein each part may have a pair of movable legs, the legsbeing collapsible for introduction and expandable for installation.

Installing comprises placing the prosthesis in a delivery device in acollapsed form, and releasing the prosthesis from the delivery device inan expanded form.

Installing comprises articulating a pair of hinged legs of theprosthesis from a collapsed configuration to an expanded configuration.

In another exemplary embodiment of the present invention, a method fortreating a knee joint having connective tissues including an iliotibialband, a biceps femoris, a collateral fibular ligament, and a patellartendon acting thereon, comprises installing a prosthesis in engagementwith at least a portion of one of the connective tissues to alter aforce vector applied by the connective tissues to the knee joint. Suchan exemplary method may also include one or more of the followingfeatures or steps:

The prosthesis is installed without cutting bone associated with theknee joint.

The knee joint has a joint capsule and the prosthesis is installedsuperficial to the joint capsule.

The prosthesis displaces the at least one of the connective tissues toalter the force vector.

The displacement of the connective tissues is lateral and/or anterior.

The prosthesis alters the angle of the force vector relative to the kneejoint.

The connective tissue is the iliotibial band and the prosthesisdisplaces the iliotibial band in the lateral direction.

The connective tissue is the biceps femoris and the prosthesis displacesthe biceps femoris in the lateral direction.

The connective tissue is the collateral fibular ligament and theprosthesis displaces the collateral fibular ligament in the lateraldirection.

The connective tissue is the patellar tendon and the prosthesisdisplaces the patellar tendon in the anterior direction.

In a further exemplary embodiment of the present invention, a method oftreating inflammation or pain due to rubbing or pressure of soft tissueagainst other tissue, comprises implanting a prosthesis proximate thesoft tissue wherein the prosthesis displaces the soft tissuesufficiently to reduce the inflammation or pain. Such an exemplarymethod may also include one or more of the following features or steps:

The prosthesis displaces the soft tissue in a manner which reduces thepressure of the soft tissue against the other tissue.

The soft tissue is the iliotibial band.

The other tissue is the lateral femoral epicondyle.

The prosthesis is implanted between the tibia and iliotibial band todisplace the iliotibial band laterally or anteriorly.

Securing the prosthesis to the tibia.

The prosthesis is secured to the tibia adjacent Gerdy's tubercle.

While the invention has been illustrated by examples in various contextsof treating human and animal osteoarthritis and dysplasia associatedwith force imbalances in a joint, it will be understood that theinvention may also have application to treatment of focal defects causedby trauma or other reasons. In particular, pain associated with focaldefects in the medial condyle in the knee may be reduced by applying thedevices and methods of the invention to reduce loading on the medialcondyle.

Other applications of devices and methods of the invention include usein conjunction with meniscal repair treatment to reduce loading on themedial condyle. The contoured bearing surface for the iliotibial bandcould also alleviate pain associated with the iliotibial band frictionsyndrome. Another application includes use in conjunction with total hipreplacement devices to alter the mechanical forces on the new joint,thereby increasing the stability of the replaced joint and reducing therisk of implant wear. The invention may further be adapted to displacetissues acting on various other joints so as to reduce or otherwisealter loads therein, including the elbow, shoulder, wrist, fingers,spine, ankle, interphalangeal joints, jaw or other joints. For example,the implants of the invention may be configured for attachment to theacetabulum, vertebrae of the spine, scapula, humerus, radius, ulna,carpals, metacarpals, tarsals, metatarsals, talus or other bones of thefoot, among other bones.

Exemplary embodiments have been disclosed above and illustrated in theaccompanying drawings. It will be understood by those skilled in the artthat various changes, omissions and additions may be made to that whichis specifically disclosed herein without departing from the spirit andscope of the present invention.

What is claimed is:
 1. A method of treating a knee joint, said jointincluding femur and tibia bones with facing articular surfaces inlateral and medial compartments, the bones being subject to a forceexerted by target tissues around said joint, the target tissue beingsoft tissue outside the joint selected from connective tissue andmuscle, the method comprising: implanting a prosthesis on the femur todisplace said target tissue laterally between about 10 mm to about 30 mmrelative to the joint, wherein a force exerted by said target tissue isredirected in a manner to redistribute a load acting on the facingarticular surfaces to reduce loading in the medial compartment of theknee without cutting said bones.
 2. The method of claim 1, wherein thetarget tissue is displaced laterally relative to its natural path. 3.The method of claim 1, wherein the prosthesis is implanted on the sameside of the joint as the target tissue.
 4. The method of claim 1,wherein the target tissue is further displaced anteriorly or posteriorlyrelative to the joint.
 5. The method of claim 1, further comprisingadjusting the magnitude of displacement of the target tissue after theprosthesis is implanted.
 6. The method of claim 1, wherein saidimplanting comprises placing the prosthesis outside the joint capsule.7. The method of claim 1, wherein the force exerted by the target tissueacts through a moment arm prior to displacing the target tissue and thetarget tissue is displaced by said prosthesis to substantially increasethe moment arm.
 8. The method of claim 1, wherein the force exerted bysaid target tissue opens the joint on a side opposite said targettissue.
 9. The method of claim 1, wherein said target tissue is theiliotibial band and the prosthesis displaces the iliotibial band in thelateral direction.
 10. The method of claim 1, wherein said target tissueis the biceps femoris and the prosthesis displaces the biceps femoris inthe lateral direction.
 11. The method of claim 1, wherein said targettissue is the collateral fibular ligament and the prosthesis displacesthe collateral fibular ligament in the lateral direction.
 12. The methodof claim 1, wherein said redirecting of force further comprisesalleviating pain in the knee.
 13. A method of treating an articularjoint, said joint including at least first and second bones with facingarticular surfaces, the bones being subject to a force exerted by softtissues surrounding said joint, said soft tissues comprising targettissues for treatment, the method comprising: implanting a prosthesis onone said bone in engagement with select target tissue; displacing saidtarget tissue by between about 10 mm to about 30 mm relative to thenatural path of said target tissue with said prosthesis; andredirecting, by said displacing, a force exerted by said target tissuein a manner to redistribute a load on said facing articular surfaceswithout cutting said first or second bones.
 14. The method of claim 13,wherein said implanting comprises securing the prostheses to a femur.15. The method of claim 14, wherein the articular joint includes lateraland medial compartments and said redirecting includes at least reducingload on said articular surfaces disposed within the medial compartment.16. The method of claim 15, wherein the articular joint comprises theknee, the target tissue comprises at least one of the iliotibial band,the biceps femoris and the collateral fibular ligament, and wherein saiddisplacing comprises displacing the target tissue in a lateraldirection.
 17. The method of claim 13, wherein the force exerted by saidtarget tissue is redirected in a manner to redistribute a load on atleast one of said articular surfaces without cutting or repositioningsaid first or second bones.
 18. The method of claim 13, furthercomprising opening the joint on an opposite side from the target tissueby said redirecting of force exerted by the target tissue.